Avoid lock/defer of jobs deined via ACL

This commit adds a table 'device_skip' that is used to restrict job queue
searches to avoid jobs that are not permitted on this backend via *_no ACLs,
or jobs on devices that have previously encountered multiple SNMP timeouts.

When the backend loads or a device is added, a row is added to the table if
that device should not be polled on this backend (together with the job
actions which are to be skipped/denied). When a device SNMP connect fails a
counter in the same row (or a new row) is incremented.

There is also a new report 'SNMP Connect Failures' to show the devices with
non-zero SNMP connect failure counters. A configurable limit in the setting
'max_deferrals' is used to set the threshold of no longer polling the device.

To reset the deferrals/failures count, restart the Netdisco backend (which
regenerates 'device_skip' cache entries).

Squashed commit of the following:

commit b5e32c219d
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 20:55:14 2017 +0100

    show all failed connections in report

commit ffce3cee84
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 20:12:39 2017 +0100

    only resolve fqdn once

commit cc4f680f01
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 20:10:20 2017 +0100

    Revert "only resolve fqdn once"

    This reverts commit 3d136a54de.

commit d8d082b30e
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 20:09:05 2017 +0100

    a report to show SNMP failures

commit 3d136a54de
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 19:37:58 2017 +0100

    only resolve fqdn once

commit 4550b8a84c
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 17:27:43 2017 +0100

    skipover now implicit from deferrals/actionset; fix sql where logic with better correlation

commit b51edbccd2
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 16:11:29 2017 +0100

    only abort lock if action matches badactions

commit 415559b24f
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 13:56:42 2017 +0100

    set skipover true when adding to actionset

commit 1086f2c467
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 13:50:56 2017 +0100

    fix empty actionset

commit 31962580b8
Merge: 9b2e993e 6808133b
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 13:25:08 2017 +0100

    Merge branch 'og-device_skip' of github.com:netdisco/netdisco into og-device_skip

commit 6808133bdb
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 13:19:54 2017 +0100

    in-job checks for acls are required for netdisco-do foreground actions

commit 3944dd7813
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 13:18:30 2017 +0100

    avoid extra device lookup

commit 9b2e993e0f
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 12:31:36 2017 +0100

    also delete device_skip rows when deleting device

commit b55854e91d
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 11:34:27 2017 +0100

    actions in device_skip table are now an array/set

commit 5e126eef07
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 09:36:33 2017 +0100

    typo

commit 44266f2767
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 09:14:25 2017 +0100

    *able checks within jobs should not be necessary with skiplist

commit e7c22e7d11
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 08:58:57 2017 +0100

    increment deferrals field when job is deferred

commit 88ae9c00ba
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 08:40:27 2017 +0100

    turn connect fail into defer

commit eac1857043
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Tue May 23 08:26:59 2017 +0100

    rename failures column to be deferrals

commit 96ed444bbb
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Mon May 22 22:52:51 2017 +0100

    set up list of jobs the backend instance should skip

commit 3a0019296d
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Mon May 22 22:01:50 2017 +0100

    separate out is_*able last_* checks

commit cf8589aba2
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Sun May 21 22:35:38 2017 +0100

    change from ignore to skip name

commit ed193356f8
Author: Oliver Gorwits <oliver@cpan.org>
Date:   Sun May 21 14:52:33 2017 +0100

    device_ignore table to track devices to skip in polling

share/config.yml

@@ -71,6 +71,7 @@ web_plugins:
   - AdminTask::SlowDevices
   - AdminTask::UndiscoveredNeighbors
   - AdminTask::OrphanedDevices
+  - AdminTask::TimedOutDevices
   - AdminTask::UserLog
   - AdminTask::Users
   - Search::Device
@@ -205,6 +206,7 @@ workers:
   tasks: 'AUTO * 2'
   sleep_time: 1
   min_runtime: 0
+  max_deferrals: 10
   queue: PostgreSQL
 
 dns:

share/schema_versions/App-Netdisco-DB-41-42-PostgreSQL.sql

@@ -0,0 +1,11 @@
+BEGIN;
+
+CREATE TABLE "device_skip" (
+  "backend" text NOT NULL,
+  "device" inet NOT NULL,
+  "actionset" text[] DEFAULT '{}',
+  "deferrals" integer DEFAULT 0,
+  PRIMARY KEY ("backend", "device")
+);
+
+COMMIT;

share/views/ajax/admintask/timedoutdevices.tt

@@ -0,0 +1,31 @@
+[% IF NOT results.size %]
+<div class="span4 alert alert-info">No significant events to report.</div>
+[% ELSE %]
+<table id="data-table" class="table table-striped table-bordered" width="100%" cellspacing="0">
+  <thead>
+    <tr>
+      <th class="nd_center-cell">Poller Host</th>
+      <th class="nd_center-cell">Device</th>
+      <th class="nd_center-cell">Failed Connections</th>
+    </tr>
+  </thead>
+  </tbody>
+    [% FOREACH row IN results %]
+    <tr>
+      <td class="nd_center-cell">[% row.backend | html_entity %]</td>
+      <td class="nd_center-cell"><a class="nd_linkcell"
+        href="[% uri_for('/device') %]?q=[% row.device | uri %]">[% row.device | html_entity %]</a></td>
+      <td class="nd_center-cell">[% row.deferrals | html_entity %]</td>
+    </tr>
+    [% END %]
+  </tbody>
+</table>
+[% END %]
+
+<script>
+$(document).ready(function() {
+  $('#data-table').dataTable({
+[% INCLUDE 'ajax/datatabledefaults.tt' -%]
+  } );
+} );
+</script>