If either of OS_USER_DOMAIN_ID or OS_USER_DOMAIN_NAME are present
then we don't tinker with anything. Otherwise, we should set
the USER_DOMAIN_ID to 'OS_DEFAULT_DOMAIN', as this provides a better UX,
since the end user doesn't have to specify these arguments.
Same logic applies for OS_PROJECT_DOMAIN_ID.
Closes-Bug: #1385338
Change-Id: I8a4034c16a1dd50d269f809abab8e960d5de20f7