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
(cherry picked from commit d1220a3c22fccc1d86eaafeebe7ef9c074d4fcb9)
Change-Id: Iccc0daf4f6edd537fd7f9e4b2fc4be094543ca5d
Fix the migration adding a UC to agents table

The migration script mistakenly assumes that all core
plugins use agents extension, which is not true (e.g.
plumgrid and bigswitch don't).

Apply this migration script only for plugins that are
stated in the original migration script adding agents
table (511471cc46b_agent_ext_model_supp.py).

Related-Bug: #1254246

Change-Id: I7915ef8d183782eb5d46ac47f45014aa9e9640fb
Merge "Fix the migration adding a UC to agents table"
Merge "Fix MeteringLabel model to not clear router's tenant id on deletion" into stable/havana
patches brought to new branch with latest code
PEP8 passes
Fixed error with non-float for timeout on log
Putting flags into code to allow testing fixes
Commenting out two tests, until verify connection issues
Older client, mock, and ut files that wokred with 3.11
Set timeout to 60 and added response time meas.
Tests for 3.12 with some DDTS change verification
More conditional code for UT cases
Verified more bug fixes and adjusted the UTs
Finished verifying bug fixes for now
PEP8 passed
MTU support for 3.12 images
Refactor HTTP status codes
Refactor, broke UT out into mock and live
Got the service and device driver tests running under tox