The Rados Gateway Admin OPS API has changed its behavior from Nautilus
to Pacific. Calling user create on an existing user wil generate
additional keys to the user on Nautilus. Where in Pacific it will report
an error with UserAlreadyExists.
So to handle both scenarios, let's first get the user, and if the user
does not exist (NoSuchUser) we then create it.
Signed-off-by: Sébastien Han <seb@redhat.com>