Integrate netdisco-sshcollector into Worker::Plugin architecture (#489)

* Initial integration of sshcollector into Worker::Plugin architecture

 * NOT FULLY FUNCTIONAL - this is only to discuss some issues for now
 * add NodesBySSH.pm
 * update Build.PL and config.yml to integrate the new module

* Further integration of sshcollector into Worker::Plugin architecture

 * NOT FULLY FUNCTIONAL - this is only to discuss some issues for now
 * added App::Netdisco::Transport::CLI loosely based on ::SNMP counterpart
 * switched to the more prevalent two-space tabs style
 * removed various TBD items, some new ones

* Further steps to integration of sshcollector into Worker::Plugin architecture

 * cleaned up code
 * added various error handling
 * warning for bin/netdisco-sshcollector deprecation
 * device_auth allows passing master_opts to Net::OpenSSH
 * netdisco-do -D also toggles Net::OpenSSH debug

* Merged NodesBySSH.pm into Nodes.pm

 * see https://github.com/netdisco/netdisco/pull/489#pullrequestreview-205603516

* Further integration of sshcollector into Worker::Plugin architecture

 * add snmp_arpnip_also option to sshcollector device_auth
 * cleanup code

* Remove big TBD: comment from CLI.pm as doc is updated now

Build.PL

@@ -37,6 +37,7 @@ Module::Build->new(
     'Dancer::Plugin::Auth::Extensible' => '0.30',
     'Dancer::Plugin::Passphrase' => '2.0.1',
     'Dancer::Session::Cookie' => '0.27',
+    'Expect' => '0',
     'File::ShareDir' => '1.03',
     'File::Slurper' => '0.009',
     'Guard' => '1.022',
@@ -54,6 +55,7 @@ Module::Build->new(
     'Net::Domain' => '1.23',
     'Net::DNS' => '0.72',
     'Net::LDAP' => '0',
+    'Net::OpenSSH' => '0',
     'NetAddr::MAC' => '0.93',
     'NetAddr::IP' => '4.068',
     'Opcode' => '1.07',
@@ -90,8 +92,6 @@ Module::Build->new(
   recommends => {
     'Graph' => '0',
     'GraphViz' => '0',
-    'Net::OpenSSH' => '0',
-    'Expect' => '0',
   },
   test_requires => {
     'Test::More' => '1.302083',