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 parameters configure_user and configure_user_role
(default to true).

Change-Id: If3d53c2c9070691b4731142f512b1f4bb754be00
Closes-Bug: 1360232
Merge "Make user creation optional when creating service."