Big Switch: Lock consistency table for REST calls

Adds a new class to hold an SQL table lock throughout
a REST call to prevent servers in an HA deployment from
using a stale consistency hash value.

Also passes the current context down to the server manager
for every request since the consistency hash will need to
be read from the database instead of from a variable on the
server pool object.

Closes-Bug: #1328331
Change-Id: I5f8402c076d7732742c0ae4d9b9d6833d42a0b7b
Updated neutron.conf to reflect new RPC options

After oslo.messaging port, some option became unavailable to set, some
of them changed description or default values. Make sure we don't leave
anything related to old RPC layer there.

New entries are generated by calling the following from inside
oslo-incubator:

$ python openstack/common/config/generator.py -l oslo.messaging

blueprint oslo-messaging

Change-Id: I1523309cf0cd92a5d5f0b265f49979b3e47c2afa
Pass newly created router to _update_router_gw_info

pass it to _update_router_gw_info as last parameter to save
retrieving it again from the session.

Change-Id: I7fbbd675839c2874578c62dfed390d86e3b4801a
Synced log module and its dependencies from olso-incubator

Old version of 'log' module depended on oslo-incubator RPC layer
implementation. This sync is intended to copy the following fix that
makes log module use oslo.messaging.notify.log_handler if available:

  * 109e325e: Use oslo.messaging to publish log errors

blueprint oslo-messaging

Change-Id: Ieb26df4e9fbb2aa4d319c79be7510006fc8461ab
Use correct MAX_LEN constant in agent functional tests

Closes-bug: #1334922

Change-Id: I62bd12da21e778f5cca97d6280c107575d912a81
Merge "Use correct MAX_LEN constant in agent functional tests"
Add sanity check for nova notification support

Since nova notification support adds a runtime dependency on
novaclient, add an external sanity check testing the system's
ability to import neutron.notifiers.nova

Change-Id: I8a72c8763bb69a01178fc4ec91071a64a4648aab
Closes-bug: #1334412
Merge "Synced log module and its dependencies from olso-incubator"
Merge "Pass newly created router to _update_router_gw_info"
Merge "Add sanity check for nova notification support"
Merge "Updated neutron.conf to reflect new RPC options"
Merge "Big Switch: Lock consistency table for REST calls"