Enable Overlapping-IP in neutron by default.

backport for 4.1.1
removed tests, that can't pass in 4.1.* branch.

Change-Id: I74675fdbcfb5784abd9392f3f6e3e5d42868626f
Closes-bug: #1286030
Merge "Enable Overlapping-IP in neutron by default." into stable/4.1