RCBC-135 Survive running with 'GC.stress = true'

Change-Id: I45464b16eb831047456716e35d11c1c38d62b246
Reviewed-on: http://review.couchbase.org/27917
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>