Implements token expiration handling

This implements handling of token expiration. Once the token is expired,
this will request automatically for a new one.

A special case is introduced if the user specified a token when the client
is initialized: this is the auth_token_from_user. In this case, we can't
know the expiration date, so we just assume it will never expire and don't
handle it ourself.

Change-Id: I3771ff5d669da015d4aa259de422c5d81aed3eb4
Signed-off-by: Julien Danjou <julien@danjou.info>
Use oslo-config-2013.1b3

The cfg API is now available via the oslo-config library, so switch to
it and remove the copied-and-pasted version.

Removes the load of copied-and-pasted cfg from each application
in authtoken middleware.
Depends on oslo-config deployments:
Nova I4815aeb8a9341a31a250e920157f15ee15cfc5bc
Glance I4815aeb8a9341a31a250e920157f15ee15cfc5bc
Quantum I4815aeb8a9341a31a250e920157f15ee15cfc5bc
Cinder I4815aeb8a9341a31a250e920157f15ee15cfc5bc

Add the 2013.1b3 tarball to tools/pip-requires - this will be changed
to 'oslo-config>=2013.1' when oslo-config is published to pypi. This
will happen in time for grizzly final.

Change-Id: I18c450174277c8e2d15ed93879da6cd92074c27a
Merge "Implements token expiration handling"
Merge "Use oslo-config-2013.1b3"