Remove unused oslo.config import

Commit 46e88320e6e6231550f3e2b40312c51f55e059f5 added
the oslo.config import in one of it's patch series but
in the revision that was ultimately merged, the import
was no longer used - but we forgot to remove the import.

This cleans that up.

Change-Id: I3fcfdab625be68a19162b5053ad4f6f180a72a4d
Add more information to generic _add_floating_ip exception message

When we fail in some unexpected way in the _add_floating_ip method it'd
be good to have more information in the error message that's passed back
to the caller so they don't have to dig into the logs for the variables
involved, especially since the fixed IP might not be provided on the
request.

We're seeing messaging timeouts in the gate and it'd be nice to have the
error information right up front so we can fingerprint on it in
elastic-recheck.

Related-Bug: #1349590

Change-Id: I7c19c5c1bc5d41a922435d78aca0160c45130276
db: Add @_retry_on_deadlock to service_update()

Add the _retry_on_deadlock decorator to the service_update() method of
nova's sqlalchemy API.  This decorator is scattered throughout the
sqlalchemy API for other methods that may encounter this error.  The
referenced bug report shows a trace from where it occurred on this
method.

Change-Id: I93b370d6457d2e85493be01a62a76404d228a6fa
Closes-bug: #1370191
Merge "Add more information to generic _add_floating_ip exception message"
Merge "Remove unused oslo.config import"
Merge "db: Add @_retry_on_deadlock to service_update()"