Drop and recreate FK if adding new PK to routerl3bindings

Since MySQL 5.6 FK columns cannot be altered. As a workaround we can
drop the FK before ALTER COLUMN and then recreate it.

Change-Id: Icd1b3075cf29a6b0c477a4ddea2e6ebee91baef8
Closes-Bug: 1384555
(cherry picked from commit b5f1cc48b877caaebc944154d56a8bb4060aa9b0)
Fix context.elevated

The current version of elevated method sets for the original context
the admin role too. This change fix this.

Added unittest.

Closes-bug: #1386932

Change-Id: Ife881112efa151e53bfa4b7af35643dcf2d1114f
(cherry picked from commit 98fae47ad1b9b72e41d444ce6f96cf5f2a3b6f0c)
linuxbridge-agent: make vxlan unicast check more efficent

A list with the full range of vxlan VNIs (1 to 2**24) was using
over 300MB of memory. This patch uses xrange instead of range.

Closes-Bug: #1393362
Change-Id: I21ccab758e7911712690fd5e732f64361e809264
(cherry picked from commit 0bf69ad80fb77773e767e116357cf6e1666b3f5d)
Merge "linuxbridge-agent: make vxlan unicast check more efficent" into stable/juno
Merge "Fix context.elevated" into stable/juno
Merge "Drop and recreate FK if adding new PK to routerl3bindings" into stable/juno