Fix Host getting disconnected from Cluster when migrating a VM in RHEV

[agrare]

When building a minimal host hash for migrated vm targeted refresh include the ems_cluster with the host so that it doesn't clear the ems_cluster_id when saving.

#13511 fixed saving a VM when it gets migrated to a new host but as a result the cluster link to that host got cleared when it was saved. This adds the cluster link to the minimal host hash so that it is saved properly.

https://bugzilla.redhat.com/show_bug.cgi?id=1420003

[agrare]

cc @borod108 @durandom

[miq-bot]

Checked commit agrare@b448a14 with ruby 2.2.6, rubocop 0.47.1, and haml-lint 0.20.0
2 files checked, 0 offenses detected
Everything looks good. 👍

[agrare]

Hey @durandom so I think the reason it is clearing the host's ems_cluster is this https://github.com/ManageIQ/manageiq/blob/master/app/models/ems_refresh/save_inventory_infra.rb#L137

It will set h[:ems_cluster_id] to nil even if h[:ems_cluster] wasn't specified. What do you think of only setting the :ems_cluster_id if :ems_cluster was specified? That seems cleaner than having to add the cluster to the host when it shouldn't be needed.

[oourfali]

Seems like automation was successful so I think we're good to go.

[borod108]

Looks great to me. Since the automation already passed I would suggest leaving this as is and merging, and implement the other, cleaner, way of solving this in a separate PR.

[agrare]

@blomquisg can you review?