NVP plugin: Avoid timeouts if creating routers in parallel

There is a well-known issue of eventlet causing deadlocks with
mysql transactions; such condition might occur when
creating NVP routers in parallel.

To avoid this, this patch moves the long-running method
_update_router_gw_info outside of the mysql transaction, adding
the appropriate failure management code, and adds a lock to the
method _nvp_create_ext_gw_port, to ensure serial access to it.

Unit tests for verifying correct behaviour in case of failures
are added as well.

Closes Bug: #1251847

Change-Id: I2864e2f5bfd3982875ef9df97186f64a9fcaa0e0
Include lswitch id in NSX plugin port mappings

This patch adds the logical switch identifier in the model class
for describing mappings between neutron and nsx switch ports.
This will allow for a better handling of the chained logical switch
use case.

This patch also moves the routines for retrieving nsx identifiers
in a separate module in preparation for the introduction of async
operations and renames relevant model classes, attributes, and
functions from 'nvp' to 'nsx'.

Related to blueprint nvp-async-backend-communication
Related to blueprint nicira-plugin-renaming

Change-Id: I5fa1e8f0d863b7d1fc278ffdeac8acc076a843e8
Imported Translations from Transifex

Change-Id: I2b76e7d72593ce2ae6b1299257a917f01d8788ea
NVP: propagate net-gw update to backend

When a network gateway's name is updated, propagate the
update to the backend.

Closes-Bug: #1261334
Change-Id: Icaae84e7f5373946e8c82e0e519528409925dd9d
Merge "Imported Translations from Transifex"
Merge "NVP plugin: Avoid timeouts if creating routers in parallel"
Merge "Include lswitch id in NSX plugin port mappings"
Merge "NVP: propagate net-gw update to backend"