Deleting HA router with attached port causes DB inconsistencies

Deleting HA router with attached port causes DB inconsistencies

When a HA router is being deleted with 'python-neutronclient'
while it has an attached interface the deletion will fail since
the router is in use. The order in which the deletion
is done is - first remove the HA interfaces from DB and
then delete the router. In this case the HA interfaces were
indeed deleted but the router itself was not (router is in use).
This causes the DB to be inconsistent where an HA router
exists in the DB while it's ports were removed from the DB.

This patch simply deletes the router first, and then
we know it's safe to remove it's HA interfaces as
well. If the router is in use and deletion fails
the HA interfaces remain intact.

Closes-Bug: #1402698

Change-Id: I956d0094ae6e2412e859d79feeb4003941d2bb4b