Big Switch: Import DB module in unit test

Import the portbinding db module in the Big Switch base test case
so the table gets created before the test is run. Otherwise the
tests will fail when being run with testtools because the portbinding
db isn't normally imported until a function call from the Plugin.

Closes-Bug: #1331240
Change-Id: Icbd2248a0c013c142ccf9b302a1ffa15c5a4e5ae
Add logging for NSX status sync cache

This patch simply adds some log statements with debug
severity for tracking events related to the NSX object
cache kept by the operational status synchronization
thread.

This will  be helpful when debugging error conditions.

Change-Id: Ieb7b44b1117048c126d275dea2b8503b85eaba04
Related-Bug: 1329560
Notify systemd when starting Neutron server

systemd is notified only when Neutron is started with multiple api
workers. This patch adds systemd.notify_once() call when starting
Neutron server with api_workers=0

Change-Id: I95581dc5dffde6168c68d9f04cf8bdfcdb773ba8
Closes-Bug: #1330532
Merge "Add logging for NSX status sync cache"
Merge "Notify systemd when starting Neutron server"
Merge "Big Switch: Import DB module in unit test"