Edge driver: Improve exception handling

Improve exception handling in the edge driver code.

Partial-Bug: #1305032

Change-Id: I727a7389aff216c4347de5605b8b1979d3e5a94e
Properly apply column default in migration pool_monitor_status

server_default parameter should be used to apply default value at
table/column creation time. Otherwise non-nullable column can't
be created because of existing rows in the tables.

Change-Id: I7136e6a0dfb9dc66ca63ff3c9fcf6de164e27e63
Closes-Bug: #1305725
Make default nova_url use a version

The default nova_url for neutron is missing an API
version number. This can cause requests to fail
because the Nova /versions API cannot respond
to Neutron notification requests.

It seems reasonable for the default value to
at least have a chance at being correct so
this patch upgrades the default Nova API url to
use the Nova 'v2' API.

Related-bug: #1298640
Change-Id: Ib1449de84fbc01fb704ebfe4a016ac8f4932be96
Fix dangling patches in Cisco and Midonet tests

Cisco Nexus Tests:
Explicitly stops the patch to sys.modules immediately
after use to fix sporadic failures caused by the patch
not being handled correctly by mock.patch.stopall.

Midonet Interface Test:
Removes the double-patch of the 'device_exists' method
in ip_lib.

Closes-Bug: #1307025
Closes-Bug: #1307038
Change-Id: Ie22505bb8e406a61e40819d60c76d229916a6e01
Merge "Make default nova_url use a version"
Merge "Fix dangling patches in Cisco and Midonet tests"
Verify ML2 type driver exists before calling del

Verifies that an ML2 type driver exists for a given
segment type before attempting to call the release_segment
method on it. Logs an error if a type driver is not
found.

This covers the case where a segment is created with
a given type and then ML2 is reconfigured without
support for that type.

DocImpact
The ML2 documentation should be updated with a warning
that disabling a network type driver and re-enabling
it later may lead to possible DB inconsistencies.

Closes-Bug: #1292102
Change-Id: I65a35abf3ed57347bb6e8fee228f8c0697217c00
Merge "Properly apply column default in migration pool_monitor_status"
Merge "Edge driver: Improve exception handling"
Merge "Verify ML2 type driver exists before calling del"