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: I8f6d6f3903b9140bf22c676b3661c2dda5766db6
Merge "Make user creation optional when creating service."