Refactor make_module for tests
The original motivation for this refactor is to reuse make_module and
drop TestMMDResolver._make_mmd. Some tests require a modulemd created
and some tests also require those modulemd to be stored into database as
a module build. The problem is db_session has to be passed to
make_module even if no need to store into database.
Major changes in this patch:
* Argument db_session is optional.
* Arguments requires_list and build_requires_list are replaced by a
single argument dependencies which is a list of group of requires and
* A new make_module_in_db is created for creating and storing the new
modulemd into database conveniently.
* Tests are updated with the new make_module and make_module_in_db.
Signed-off-by: Chenxiong Qi <email@example.com>