Fix for admin grant backfill scenario (#2262)
Fix for admin grant backfill scenario (#2262)

Avoids duplicate backfill when multiple admin grants are made.
couchbaselabs/sync_gateway,couchbaselabs/sync_gateway,tophatch/sync_gateway,ceejatec/sync_gateway,ceejatec/sync_gateway,tophatch/sync_gateway,tophatch/sync_gateway,couchbaselabs/sync_gateway,ceejatec/sync_gateway,couchbaselabs/sync_gateway,ceejatec/sync_gateway,tophatch/sync_gateway