Fix MeteringLabel model to not clear router's tenant id on deletion

foreign_keys parameter of orm.relationship should point to local columns.
Currently for MeteringLabel it points to Router.tenant_id column which causes
routers tenant_id clearing on label deletion.

Closes-Bug: #1249188
Change-Id: Iccc0daf4f6edd537fd7f9e4b2fc4be094543ca5d
Midonet to support port association at floating IP creation

The Midonet plugin currently does not support associating floating IPs with
ports at floating IP creation time. This bug is created to add this support.

Change-Id: Ie57ebffa5185f26138c04b9836067417c6dc1388
Closes-Bug: #1249957
Improve unit test coverage for Cisco plugin nexus code

Closes-Bug: #1190622

This fix improves the unit test coverage for the Cisco Nexus plugin's
cisco_nexus_network_driver_v2.py and cisco_nexus_plugin_v2.py
source files from:
cisco_nexus_network_driver_v2: 72%
cisco_nexus_plugin_v2:         79%
To:
cisco_nexus_network_driver_v2: 99%
cisco_nexus_plugin_v2:         94%

Much of what the remaining "uncovered" code (coverage tool
reports as partially covered) can be attributed to the
coverage tool not being aware that execution does not
continue at the end of a save_and_reraise_exception()
context block (i.e. the exception will be reraised, but
the coverage tool isn't aware of this).

This fix and coverage results are dependent on the fix for #1246080.

Change-Id: Ie0e11fc0a12502739fb39bb4b30deb04dd31b7b0
Merge "Midonet to support port association at floating IP creation"
Merge "Improve unit test coverage for Cisco plugin nexus code"
Merge "Fix MeteringLabel model to not clear router's tenant id on deletion"