VPNaaS: Separate validation for Cisco impl

Moving validation logic from Cisco service driver, into a
validation subclass, so that it'll be applied during the
persistence phase (so validation failures can block the
persistence, instead of setting to error state).

This is part of the effort to separate out L3 validation
and builds upon the reference implementation changes being
reviewed in 102351.

Note: One unit test is commented out, due to a bug in
oslo.messaging 1.3.0. It will be uncommented later, once
1.4.0.0.a3 or newer is available for use.

Change-Id: I6040e6d8ab32b707bcf67a0882507b7ee2d4bebe
Partial-Implementation: blueprint l3-svcs-vendor-validation
Merge "VPNaaS: Separate validation for Cisco impl"
Set python hash seed to 0 in tox.ini

New tox (>=1.7.0) sets a random python hash seed by default. This is
generally good for testing because it will help keep projects working
regardless of the hash seed, but neutron unittests don't currently pass
with a random hash seed so set it to the python default seed.

This change will allow us to use new tox again and remove the
restriction on tox<=1.6.1 to run unittests.

Note this change will need to be backported to the stable branches to
keep unittests there working with new tox as well.

Change-Id: If151efeb8caae3111515191e238d6e6ae491cd44
Merge "Set python hash seed to 0 in tox.ini"