Temporarily use heat's heat-keystone-setup-domain

Heat in juno relies on keystone domains, however our lxc keystone module
does not support this functionality (which requires keystone v3).  Our
long-term goal should be to update our keystone ansible module however
there are larger implications in moving that module over to using v3
for all calls.

This commit bypasses using the keystone module and shells out to
heat-keystone-setup-domain which sets up the keystone domain and domain
user for us.