Fix missing migration default value

Fix 128e042a2b68_ext_gw_mode and 40b0aff0302e_mlnx_initial
migrations by properly using server_default parameter in column
definitions.

Change-Id: I199e206dccc36fcfc2457a17167c76611d69784a
Closes-bug: #1336556
NSX: neutron router-interface-add should clear security-groups

NSX does not support security groups on router ports so in the case
where someone uses a port that has a security group on it as the router
port we need to clear the security group off the port.

Change-Id: Ia0fb331516887dcd7e9a435094ce1eb082d72575
closes-bug: 1329043
Remove reference to setuptools_git

It is not needed for any purpose and was superseeded a while ago.

Change-Id: I53f318cc49916afeea749d4fd8aa5a0bafa567a7
Remove dead helper function from test_l3_plugin

This code is no longer used anywhere, so it
can be safely removed.

Change-Id: I23cc2e2cafda2408c98e052a6667cd303335331f
Extract CommonDBMixin to a separate file

db_base_plugin_v2 imports too much modules that are not necessary
usually, so extract CommonDBMixin in different file.
Plus using db_base_plugin_v2 for some types of modules can lead to
cycles in imports, this refactoring should resolve the issue.

Closes-Bug: #1340145
Change-Id: Idb027d7c5cee2d5bc7598f805c56c55fd4aca048
Add 'server_default' parameter

If a model mentions 'default' it is better to set 'server_default'
as well because this 'defaut' can be reached only via code. This
change adds 'server_default' parameter to models and in database,
so if someone will use SQL query it will also use default value.

For model Router added parameter server_default. In migration it was
added by this change https://review.openstack.org/105212.

For model MeteringLabelRule added parameter server_default.
In migration it will be added by heal script due to problems
with Metering plugin and grenade.

Partial-Bug: #1295539

Change-Id: Iab6fb4eca73e4918c16dac2945fd8552ae2a0c73
Merge "NSX: neutron router-interface-add should clear security-groups"
Merge "Fix missing migration default value"
Merge "Add 'server_default' parameter"
Merge "Remove reference to setuptools_git"
Revert "VPNaaS REST Client UT Broken"

I8badc249ad021fdbdb2367b5416c72435ed58994 causes anything importing
neutron/tests/unit/services/vpn/device_drivers/_test_cisco_csr_rest.py
to exit since httmock isn't a dependency.

Fix all hacking issues in addition to the revert, as this patch fixes 'tox -epep8'.
And just a reverting the patch will cause pep8 to fail.

Fixes-Bug: #1340881

This reverts commit 7f0a8f09ab7867100081a898347a5f901e5a442b.

Change-Id: I373a8c8ab16eb387be6a451b8146642389081afa
Merge "Remove dead helper function from test_l3_plugin"
Merge "Revert "VPNaaS REST Client UT Broken""