Add additional mock-compatible HTTP tests

These tests use the admin API, which is available on the mock

Change-Id: I183df65bcdb2ae8f7d6c55c8df246bfb6534e4e0
Reviewed-on: http://review.couchbase.org/42615
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>