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
Migration 148: Fix drop table dependency order

The downgrade of 148 was broken because instance_actions_events has a FK
dependency on instance_actions but was attempted to be deleted first,
which caused the sqlalchemy to complain.

The fix is to reorder the table deletes in the downgrade.

Additional cleanups:

* Remove unecessary exception handling which masked errors

Change-Id: Iaac77ba0e81071f6bb39e5cc3b599a4138eb3cd2
Actually run baremetal migration tests.

The baremetal migration tests weren't being run because the test lookup
code was looking for a tests of form 'check_#' instead of 'check_###'.

Change-Id: I8f162d6493dd09b2d0cff36c40ae9acc5df1269c
BM Migration 004: Actually drop column

SQLAlchemy-migrate appears to support passing in a Column or a
column-name string into `drop_column`. In practice though, only the
column-name form actually works.

Change-Id: I1bcc28511d652df44f7168fb84c8be7dacd60cfd
Merge "Migration 147: Prevent duplicate aggregate_hosts"
Merge "Migration 148: Fix drop table dependency order"
Merge "Actually run baremetal migration tests."
Merge "BM Migration 004: Actually drop column"