Use packstack fork of puppet-keystone

Upstream does not have important fix [1],
which is blocking some tests. We will have
to use fork [2] until mentioned quickfix will
be merged or real fix will be merged.

[1] https://review.openstack.org/#/c/53661
[2] https://github.com/packstack/puppet-keystone/commits/packstack/havana

Change-Id: I8779a2955ea856cdb6991f02e36ce385eef6e3f2
Fixes: rhbz#1022686