Add tools/create_heat_domain helper script

For users who don't yet have python-openstackclient, or who require
a more automated way of creating the heat domain and domain-admin
user, provide a simple wrapper for the keystoneclient python API
which will create the domain and user, then print a helpful cut/paste
message to allow heat.conf to be easily updated.

It requires a cloud-admin users credentials to be sourced in the
environment, OS_USERNAME/OS_PASSWORD/OS_AUTH_URL and also a script
specific variable HEAT_DOMAIN_PASSWORD which specifies the password
for the domain-admin user.  Other values may be overridden by the
environment but default to sane values.

Change-Id: I5731ba72491dcf515c5d230b55056d9263341c54
Partial-Bug: #1287980
Merge "Add tools/create_heat_domain helper script"