[GSI] index scan times out for scan_consistency=at_plus and scan_vector_per_values=1.0

Testrunner command: ./testrunner -i /tmp/tuqvm.ini doc-per-day=50,nodes_init=4,get-cbcollect-info=True,get-logs=True,stop-on-failure=False,get-coredumps=True,gsi_type=forestdb -t 2i.indexscans_2i.SecondaryIndexingScanTests.test_primary_query_scan_consistency,groups=simple,dataset=default,doc-per-day=20,use_gsi_for_primary=True,use_gsi_for_secondary=True,scan_consistency=at_plus,scan_vector_per_values=1.0,nodes_init=4,services_init=kv:n1ql-kv-kv:index-index

Error Message:
N1QLQueryException: unable to get expected results for query CBQError: host 172.23.106.75: ERROR:{u'status': u'errors', u'errors': [

{u'msg': u'Index scan timed out from 172.23.106.78:9101 - cause: Index scan timed out from 172.23.106.78:9101', u'code': 5000}

], u'results': [], u'metrics':

{u'elapsedTime': u'4m0.048034085s', u'executionTime': u'4m0.047926292s', u'resultSize': 0, u'resultCount': 0, u'errorCount': 1}

, u'requestID': u'500251bb-3b20-4d03-b1d6-c6b1886d4a17', u'signature': {u'': u''}}

Testrunner Log: http://qa.sc.couchbase.com/job/cen006-2i-vset00-02-scan-consistency-single-bucket/241/consoleFull