Move auth_token config to .conf, key cache directories

auth_token configuration can now be read from the conf files
rather than the paste.ini files.

A key cache directory has been created for each of the 3 API services
under /var/cache/heat

This is the devstack change relating to
Heat Blueprint: keystone-middleware

This is related to this committed change:
https://review.openstack.org/#/c/26351/

Devstack users will find Heat to be broken until this corresponding change
is approved.

Change-Id: If6f77f86a3eeb08a58b516725bd806e39ccedb50
Merge "Move auth_token config to .conf, key cache directories"