Only create swift account if swift enabled

Only call the swift account creation function if swift is enabled,
otherwise the endpoints are created in keystone even though swift
isn't running.

This causes failures when tempest queries keystone and thinks swift is
there; it starts running tests against it that fail with unhelpful
"connection refused" errors.

Change-Id: Icf08409c9443ec703e5f1da4531aa34c326f3642
Merge "Only create swift account if swift enabled"