This commit switches to using the oslo.log library instead of the
locally synced version from oslo-incubator. Also, since Tempest-lib
doesn't actually use oslo.config for anything except oslo.log now
that we're using it as an external lib let's remove oslo.config from
the requirements file.
Change-Id: Ia4f12b747643637d93bf6873563b6c34924c5bb0
a45b4da5e1