CBQE-0: Fix _get_indexer_task_pid

unable to check index on server 10.3.4.66 because of _get_indexer_task_pid() takes exactly 2 arguments (3 given)

Changed to right number of arguments

Change-Id: I2bb4b3a51be5750cfab9fe6da15e73ddd4afc07f
Reviewed-on: http://review.couchbase.org/32712
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>