Embrane Tempest Compliance

This changeset tracks the changes needed by the Embrane's Neutron Plugin
in order to consistently  pass tempest tests.

Changes:

- Some db transactions were too long and were causing lock timeout
exception. Removed useless transactions (waiting on non-db tasks to complete)
to fix the problem.

- The operation filter was useless, and breaking the tests. Most of the
logic which guarantees the appliance correct state when an operation in executed
is now in the internal library used for the heleos APIs.
The filter was therefore removed (as well as the corresponding exception).

- Fixed "sync" mode. The behavior was incorrect due to the queue timeout.
Furthermore, parallel requests were not waiting on the correct thread.

- Added missing methods for floating IPs (not all the scenarios were covered).

- Minor bug fixes caught during the tests.

Change-Id: If081b50b4629158016ba421b94612a4cfac82257
Closes-Bug:1269098
BigSwitch: Use backend floating IP endpoint

Adds new floating IP REST calls for backend
controllers that support it. Adds backend
capability discovery mechanism.

Implements: blueprint bsn-floating-ip-endpoints
Change-Id: I2301d62a05d256867255865556625603918e84cf
Merge "BigSwitch: Use backend floating IP endpoint"
Merge "Embrane Tempest Compliance"