Migration 147: Prevent duplicate aggregate_hosts

If an aggregate_host record is already present, then the `upgrade`
shouldn't attempt to add it again.

Change-Id: Ib7ab10fa7c166ccaa3df6a96eb08c7ebcd0af38c
Merge "Migration 147: Prevent duplicate aggregate_hosts"
Merge remote-tracking branch 'm_src_repo/master' into build-temp