Make test_snapshot_pattern ssh error path work

When validation was added to all ssh connections this means that the
exception handling code around ssh connections was actually run, a bug
was fixed in the exception logging for test_snapshot_pattern. It also
reraises the error so we know that the failure was caused by the ssh
connection

Change-Id: Iadccef5046e8884fce54ba2cea591a6e86a8b318
Merge "Make test_snapshot_pattern ssh error path work"