Use log_depot for MiqServer#log_file_depot or Zone#log_file_depot
Use log_depot for MiqServer#log_file_depot or Zone#log_file_depot

When the Zone level log_file_depot is configured, but not the MiqServer, MiqServer#log_file_depot is nil, so we need to look for the Zone's depot.

Commit 4f0c1b542649bb8b4c99d8f584582aeef439cefa, changed log collection to use relationships to get the file depots but only on the server.
It missed that we can configure the depot at the server or zone or both and that we should look for the server's first, then the zone's.

https://bugzilla.redhat.com/show_bug.cgi?id=1186485

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