heat-db-setup read engine config file for DB connection details

heat-db-setup read engine config file for DB connection details

Currently heat-db-setup, or rather the underlying python -m heat.db.sqlalchemy.manage
has a hard-coded database connection URL, so DB setup will fail if a non-default
configuration exists in /etc/heat/heat-engine.conf.

This attempts to read the sql_connection from the DEFAULT section of heat-engine.conf
falling back to the old default string on failure.

bug/1087741

Change-Id: Ieb41503a58ee0804d79a32a8286268803c9f456c
Signed-off-by: Steven Hardy <shardy@redhat.com>