Disable MockUnitTest.testPurgedBody temporarily

Change-Id: Ic5f37892771efbb19266bb1b946a8ad5f24cfa3e
Reviewed-on: http://review.couchbase.org/27532
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>