Big Switch: Don't clear hash before sync

This patch removes the step of clearing the consistency
hash from the DB before a topology sync. This will ensure
that inconsistency will be detected if the topology sync
fails.

This logic was originally there to make sure the hash header
was not present on the topology sync call to the backend.
However, the hash header is ignored by the backend in a sync
call so it wasn't necessary.

Closes-Bug: #1379510
Change-Id: I2d58fa2aea3b692834d64192d06ace727c7df8a0
Update VPN logging to use new i18n functions

For log messages in neutron/services/vpn and neutron/db/vpn, replace
_() marker functions with log-level-specific marker functions: _LI(),
_LW(), _LE() from oslo.i18n.

Also, remove _() functions for debug log messages as debug level log
messages should not be translated.

Change-Id: I07fcf25bb6344c47e74d6ee23f9bc08e4b560679
Closes-Bug: #1379811
Handle unused set_context in L3NatTestCaseMixin.floatingip_with_assoc

set_context which is passed to floatingip_with_assoc method
is not passed further to self._make_floatingip.

Change-Id: Iecf2ad88e4bad5b1f8fd60668401863bdeecce8f
Closes-Bug: #1378756
Catch exceptions in router rescheduler

Catch and log exceptions in router rescheduling loop
rather than just dying which would stop all future
router rescheduling attempts.

This prevents transient DB connectivity issues from
permanently breaking the rescheduler until the process
restarts.

Closes-Bug: #1375597
Change-Id: I2ab37847074fa6bbdd2b13fd03b8742996dcfc78
Merge "Update VPN logging to use new i18n functions"
Merge "Big Switch: Don't clear hash before sync"
Merge "Handle unused set_context in L3NatTestCaseMixin.floatingip_with_assoc"
Merge "Catch exceptions in router rescheduler"