Support for cross-plugin conditions

[Michael Polenchuk]

Environment:
 latest 9.0 iso with ODL plugin

Steps to reproduce:
 * create new env with ODL plugin enabled
 * try to change some settings Other->OpenDaylight plugin
 * save <- failed (src: http://paste.ubuntu.com/16833847/)

Actual result:
 Gently failed with just one line in api.log
 Response code '500 Internal Server Error' for PUT /api/clusters/1/attributes from 127.0.0.1:53353
 on "condition":"settings:bgpvpn == null or settings:bgpvpn.metadata.enabled == false"
 (https://github.com/openstack/fuel-plugin-opendaylight/blob/master/environment_config.yaml#L43)

 It happens due to bgpvpn plugin absence.

Expected results:
 Settings saved w/o errors or UI showed an error message w/ restriction.

Additional information:
 https://github.com/openstack/fuel-plugin-opendaylight

[Dmitry Pyzhov (dpyzhov)]

This bug seems to be not related to Fuel project itself. Marking as incomplete.

[Arthur Svechnikov (asvechnikov)]

This bug is related to Fuel. This bug occurred due to an error in the validation of cluster attributes restrictions. RestrictionBase uses `strict` by default, however, there is no other option how to check whether some plugin is installed or not, only "settings:some_plugin == null". In this case, BaseRestriction will raise the error that settings doesn't contain some_plugin entity.

[Dmitry Pyzhov (dpyzhov)]

Fuel doesn't support cross-plugin dependencies at the moment. Marking this request as a feature request for the next release.