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: I6b0b7e2554e982550d71d8427ce2ea94f04f55e8
Closes-Bug: 1360232
Merge "Make user creation optional when creating service."