Peg the version of Ming used in tests

Up until today we have needed to use a git checkout of Ming
to get some changes we pushed upstream but that were not
released. Release 0.3.2 includes all of our changes, so we
can now update our requirements to use it and stop using
the git head.

Change-Id: I4a3c242259c279b1e1be86d280572dd8cd26e84e
Signed-off-by: Doug Hellmann <doug.hellmann@dreamhost.com>
Merge "Peg the version of Ming used in tests"