heat api : add register_api_opts to init.py

Add register_api_opts to api/__init__.py, slightly simplifying
the api executables, and also solving an issue with some tests
which were not working via nosetests -s due to the required
options not being registered in cfg.CONF

Change-Id: I70b16aae1f73f72518013dbcda37defa79fc5649
Signed-off-by: Steven Hardy <shardy@redhat.com>