Add upgrade test for Riak Control

Some issues have been found when running a mixed cluster with Riak
Control enabled.  This tests the typical upgrade scenario of a
customer and verifies that Riak Control at least doesn't crash any of
the nodes while in a mixed cluster state.

See https://github.com/basho/riak_control/pull/120
Merge pull request #342 from basho/rz-riak-control-upgrade

Add upgrade test for Riak Control