Ems event groups - allow provider settings (deeper_merge edition)

[durandom]

Allow provider plugins to participate in setting up EmsEvent.event_groups

In order to provide settings for event_handling.event_groups every provider had to include its event names into settings.yml - which grew massively to beyond recognition.

To split these into settings.yml in the provider repos I have to hook into the event_groups method (see [1] for reasons).
This patch iterates over all registered provider plugins and looks for the same event_handling.event_groups structure under the provider name key.

Eg.

:ems:
  :ems_amazon:
     :event_handling:
        :event_groups:
          :addition:
            :critical:
            - AWS_EC2_Instance_CREATE
            - AWS_EC2_Instance_UPDATE
            - AWS_EC2_Instance_DELETE
          :power:
            :critical:
            - AWS_EC2_Instance_running
            - AWS_EC2_Instance_shutting-down
            - AWS_EC2_Instance_stopped

Then it merges the hash and more important merges the arrays of events.

Follows the suggestion in [1]

[1] ManageIQ/manageiq-providers-amazon#138

This is the same as #13942 - just with DeepMerge.deep_merge!

[durandom]

@miq-bot add_labels enhancement, pluggable providers
@miq-bot assign @Fryguy

[miq-bot]

Checked commit durandom@afb3b91 with ruby 2.2.6, rubocop 0.47.1, and haml-lint 0.20.0
3 files checked, 0 offenses detected
Everything looks good. 🍪

[Fryguy]

Should this be core_event_groups?

[durandom]

nope, its each_with_object(core_event_groups) and event_groups is the memo object...

[Fryguy]

Ah ok, I missed that bit