Remove any specific 1.2.1 code.

Unfortunately, this drastically reduces the value of the test because is
no longer verfies a "liveness" property of capabilities; it doesn't
verify that things will negotiate to the newer version.  However,
leaving the remainder of this test in place verifies two things: a.)
"safety", things do not regress to a earlier capability, and that the
override capabilities work as designed.
Use eventual assert in overrides

Overrides are used when caps are renegotiated, not immediately. So it's
better to do the wait until dance to avoid a race condition.
Merge pull request #425 from basho/bugfix/csm/verify_capabilities

Remove any specific 1.2.1 code.