Add IPv6 support to scenario tests

This patch complements I4ca727f92618998242af18908bbbda6bb5f86303
by adding IPv6 functionality to scenario tests.

Also, as described in I4ca727f92618998242af18908bbbda6bb5f86303,
this change is also adding a new test config option to override
NFS access rules.

Change-Id: Id8b005cdd429d53a75624885fe7ca795746c3ede
4 files changed