lib/tempest: $HEAT_CREATE_TEST_IMAGE is not used anymore

Ridiculous patch to remove a not true anymore code comment. If
one wants to have Devstack get a heat compatible image, one
should add HEAT_FETCHED_TEST_IMAGE=Fedora-i386-20-20131211.1-sda
in his localrc

Change-Id: I2702a322fe1332be5c1301bb32710288ec683350
Merge "lib/tempest: $HEAT_CREATE_TEST_IMAGE is not used anymore"