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

lib/App/Netdisco/DB/ResultSet/Admin.pm

@@ -4,12 +4,34 @@ use base 'App::Netdisco::DB::ResultSet';
 use strict;
 use warnings;
 
+use Net::Domain 'hostfqdn';
+
 __PACKAGE__->load_components(qw/
   +App::Netdisco::DB::ExplicitLocking
 /);
 
 =head1 ADDITIONAL METHODS
 
+=head2 skipped
+
+Retuns a correlated subquery for the set of C<device_skip> entries that apply
+to some jobs. They match the device IP, current backend, and job action.
+
+Pass the C<backend> FQDN (or the current host will be used as a default), and
+the C<max_deferrals> (or 10 will be used as the default).
+
+=cut
+
+sub skipped {
+  my ($rs, $backend, $max_deferrals) = @_;
+  $backend ||= (hostfqdn || 'localhost');
+  $max_deferrals ||= 10;
+
+  return $rs->correlate('device_skips')->search(undef, {
+    bind => [[deferrals => $max_deferrals], [backend => $backend]],
+  });
+}
+
 =head2 with_times
 
 This is a modifier for any C<search()> (including the helpers below) which

lib/App/Netdisco/DB/ResultSet/Device.pm

@@ -596,9 +596,14 @@ sub delete {
       )->delete;
   }
 
-  $schema->resultset('Admin')->search({
-    device => { '-in' => $devices->as_query },
-  })->delete;
+  foreach my $set (qw/
+    Admin
+    DeviceSkip
+  /) {
+      $schema->resultset($set)->search(
+        { device => { '-in' => $devices->as_query } },
+      )->delete;
+  }
 
   $schema->resultset('Topology')->search({
     -or => [