Do not use Administrator account in tests

Fixes tests after http://review.couchbase.org/28698

Depends-On: http://review.couchbase.org/28747
Change-Id: I13b1a991519073411ee0d8fff3092331dcba6022
Reviewed-on: http://review.couchbase.org/28748
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>