Register DB options independently of engine

We need a script that will just manage database migrations (for bug
1072949), so for this purpose we want to register only the DB options, not
all of the engine options.

Change-Id: I99bb8d5800741d71572a14c3a5a33dcf0e1b0268

heat/common/config.py

@@ -119,9 +119,12 @@ def register_api_opts():
     rpc.set_defaults(control_exchange='heat')
 
 
+def register_db_opts():
+    cfg.CONF.register_opts(db_opts)
+
+
 def register_engine_opts():
     cfg.CONF.register_opts(engine_opts)
-    cfg.CONF.register_opts(db_opts)
     cfg.CONF.register_opts(service_opts)
     cfg.CONF.register_opts(rpc_opts)
     rpc.set_defaults(control_exchange='heat')

heat/db/__init__.py

@@ -15,4 +15,8 @@
 
 '''Database abstraction for Heat.'''
 
+from heat.common import config
+
+config.register_db_opts()
+
 from heat.db.api import *

heat/engine/__init__.py

@@ -15,3 +15,5 @@
 from heat.common import config
 
 config.register_engine_opts()
+
+from heat import db  # pyflakes_bypass register DB options