Fix isinstance assertions

self.assertIsInstance is preferred over assert(isinstance(..)). See feedback in:
https://review.openstack.org/#/c/102754/1/neutron/tests/unit/test_extension_security_group.py

Change-Id: I9dd6141d8f25961eb42a390b45e6d94d482afc1c
Fix UnboundLocalError raised during L3 router sync task

This can be fixed in a number of ways: a) consolidating the
two except clauses into one; b) adding a 'return' after the
last except clause c) by calling the cleanup method only on
success; d) initializing 'routers' before usage.

Approach c) has the benefit of stating the developer's intent
more explicitly and minimize chances of regression.

Closes-bug: #1336566

Change-Id: Ib91ac5bb07869cbec6825b60d7c4c5b23c4c4d3a
Omit mode keyword when spawning dnsmasq with some ipv6 subnets

Fix UnboundLocalError for certain cases of ipv6 subnets

Closes-Bug: #1335959
Change-Id: I5e4b94d9ba1b13b72e2300b53d5638968e0d3401
Add a link to a blog post by RedHat that discusses GRE tunnels in OVS

Change-Id: I6f3f458eadac12bcb907a2ee6b5d795b8e9593e2
Merge "Fix isinstance assertions"
Merge "Omit mode keyword when spawning dnsmasq with some ipv6 subnets"
Merge "Fix UnboundLocalError raised during L3 router sync task"
Merge "Add a link to a blog post by RedHat that discusses GRE tunnels in OVS"