Expand HACKING with commit message guidelines

Add a 'Commit Messages' section to HACKING describing how a commit
message should be formed.

Change-Id: I49f7c3febf65db246a84b0314597615f8d0ba247
Don't raise HTTPForbidden on a multitenant environment

When getting public images in a multi-tenant environment, Swift raises
HTTPForbidden for chuncked images.

Based on swift documentation, rlistings directive turns listings on,
which is the desired behavior in this case.

Fixes bug 1170156

Change-Id: I149f702d5b3ebae73b04deed4809939ab43c6adc
Remove unused configure_db function

DB drivers currently implement a configure_db function that is supposed
to be used for seting up the environment and getting an engine back from
it. Since it is not being used anywhere in the code but tests, I removed
it and modified tests in order to call both functions (setup_db_env and
get_engine) where/ when needed.

As pointed out in another bug, it is important to just call setup_db_env
when instantiating the db_api in order to keep it lazy. AS for
sqlalchemy get_engine will be called when a session is requested.

Fixes bug 1167770

Change-Id: I2ebeb5e8424a4857df21f7c2d5b33e8ae0100c6a
Merge "Don't raise HTTPForbidden on a multitenant environment"
Merge "Remove unused configure_db function"
Merge "Expand HACKING with commit message guidelines"