Fixes the EC2 Auth Token Settings

Previously, the module would create a keystone_ec2_uri parameter
in heat.conf.  This flag does not exist within heat.conf.
Additionally, the auth_uri within [ec2authtoken] would use the
incorrect auth uri (standard Keystone URL instead of the EC2
URI).

Change-Id: I61bcf59c60617db07eb3fad3e3e23e8fd6ab9eff