heat api: fix ec2token authentication

Since the change merged from https://review.openstack.org/#/c/27383/
ec2token auth no longer works, because there is a mismatch between
the config file section name and the section specified in ec2token

fixes bug #1174673

Change-Id: I5c0465de5c023f587b677b10717ca3a08ba411b7
Merge "heat api: fix ec2token authentication"