Make user creation optional when creating service.

In some cases it is useful to be able to just configure
the service in Keystone and not the service user. This
is the case when e.g. a read only LDAP backend is used.
Added a parameter configure_user (defaults to true).
Closes-Bug: 1360232

Change-Id: I541224b9bf431da957b9de31909e0aad5c9be187
Merge "Make user creation optional when creating service."