Moves the HA resource creations outside of transaction

Currently the HA resources are created in the
_create_router_db which includes calls to
the plugin and generates RPC calls. Even if the
resource creations are outside of any transaction
from the _create_router_db point of view, this
method is  called in a transaction from the
create_router method.
This patch moves the resource creations to the
create_router method outside the transaction.
The failures are handled as previously with
a try/expect.

Conflicts:
	neutron/tests/unit/db/test_l3_ha_db.py

Change-Id: If8fcfd012f8e992175e49bbefb2ae667881a620a
Closes-bug: #1374461
(cherry picked from commit ccd650732729451aa8e5ce3401f9570c70c4f066)
Merge "Moves the HA resource creations outside of transaction" into stable/juno