Improve Missing Manifest for unknown hosts

[treydock]

A few things to improve.

1. If hostname of an unknown host cannot be resolved by Socket.gethostbyaddr the host would not be added to missing_manifests. In my case I have to preregister DNS names which is updated once every 24-hours. This means most new systems won't resolve in DNS for at most of 24 hours.

Error like this ...

SocketError (host not found):
  app/models/missing_manifest.rb:22:in `gethostbyaddr'
  app/models/missing_manifest.rb:22:in `get_hostname'
  app/models/missing_manifest.rb:17:in `request_ip='
  app/controllers/computers_controller.rb:55:in `block in show'
  app/controllers/computers_controller.rb:48:in `show'

2. Since a host who is unknown but contacting the server likely is also running the postflight script, need to fix the checkin action for Computers to first check if a computer exists. Errors like this

NoMethodError (undefined method `managed_install_reports' for nil:NilClass):
  app/controllers/computers_controller.rb:128:in `checkin'

3. Allow management of the Missing Manifest items. Possibly allow a "one click" addition of host to known computers, also allow removal of hosts from list without adding them. A sub item to this is add Computer Group to the dashboard form.

Have # 1 and # 2 worked out..more work needed on # 3.

[treydock]

Related to this possibly, I ran into an issue where a Mac on my workbench's private network showed up as an unknown client with the DHCP server's information. The MAC was correct but the hostname showed as the DHCP server. However looking at the way Munkiserver obtains the hostname, I don't see any other method to populate that entry.

One possible alternative would be to make the assumption that if a client contacts the Munkiserver it is also attempting to send postflight system profile information. So modify the checkin method to populate some of that information into MissingManifest such as the hostname. This would get around issues where DNS cannot fullfill the entry correctly. For me this would also fix the issue of off-campus systems reporting in for the first time.