Use system locale when Accept-Language header is not provided

Remove en_US as the default language when no header is provided, and use
None instead. Upon translation None will be defaulted to system as it
was before the translation changes.

Fixes bug: #1214476

Change-Id: I0fe22c526710e69ae0731e7d0b42170e6f3a8523
Deal with 501 errors from NVP correctly

This is done by adding the error code to the exception
handlers dictionary as done for other error codes.

Fixes bug #1215583

Change-Id: Ic876c6bccaf94cae626dfc908c4a34dfbcead406
Fix port creation issue appeared with postgresql backend

IPAllocationPool has relation to IPAvailabilityRange which is setup to
load eagerly. Eager loading is implemented with left outer join which is
incompatible with with_lockmode('update') on postgresql.
The fix redefines eager loading with options(joinedload) making it use
inner join.

fixes bug 1215350

Change-Id: I148d37f2a1c2a340327d36c240eb8173aee9219a
Separate l3 db tests for l3 agent into their own test case

Bug 1215871

This patch does a simple refactoring of test_l3_plugin, pushing out tests
aimed at validating the interactions of the l3 agent with the server.

These tests explicitly use TestL3NatPlugin, whereas all the
other tests use a configurable plugin, which might be specificed by a child
class. This might lead to confusion and possibly errors in unit tests for
child classes, especially those not using the l3 agent - for which running
these test is also superfluous.

Change-Id: Ia9ed320ea775fc548e6a5b711c67c9f3b0ae2f6d
Imported Translations from Transifex

Change-Id: I9300e32b84f02492c8cf32cfff65f3eb207672d5
Merge "Separate l3 db tests for l3 agent into their own test case"
Merge "Use system locale when Accept-Language header is not provided"
Merge "Deal with 501 errors from NVP correctly"
Merge "Fix port creation issue appeared with postgresql backend"
Add l2 population base classes

This patch initiates the blueprint l2-population

OVS & LinuxBridge drivers will be added as dependencies.

Change-Id: Ia2345aa262ec791c9f38b6e41e1e4b46f69cadac
OVS agent implementation of l2-population

This patchset implements l2-population RPC callbacks in OVS agents,
it enables plugin to populate forwarding table following portbindings
events.

For now, it doesn't include ARP responder implementation which is
deferred to a future patchset (As this feature isn't yet supported by
OVS, it will require the use of an external responder such as ebtables)

It anyway brings some improvements in tunnelling management, as agent
will tear-down unecessary tunnels, and flood packets on a per-network
basis rather than to all other agents.

These changes should anyway have a limited risk, as tunnel management
won't be affected as long as plugin doesn't implements l2-population.
If this feature is activated on ml2 plugin, it'll stop sending tunnel
endpoints to agents, and use the new RPC callbacks.

Implements: blueprint l2-population

Change-Id: I5185eefedb0ff392bc8b99d16f810813e26ff58d