Pass Full Credentials to Engine

Pass Full Credentials to Engine

In order to support HA operations, eg restarting an instance, we
need to have full credentials in the engine.  This patch passes
in the credential information into the engine and uses it to validate
the the user.  A future patch will have this information stored in
database and associated with each stack.  It also assigns the username
in the case of EC2 style authentication allowing us to support
per-user stacks with EC2 auth.

Change-Id: I4b92f83d4d10a2bfebd4ddedc8a4f53b3e1217fe
Signed-off-by: Ian Main <imain@redhat.com>