extend lock while ingesting items (#1925)
extend lock while ingesting items (#1925)

when migrating instances there are long running
ingest processes during which initial lock
expires and then another process starts ingesting
same content and possibly creates duplicates.

SDESK-5393
petrjasek/superdesk-core,superdesk/superdesk-core,superdesk/superdesk-core,petrjasek/superdesk-core,petrjasek/superdesk-core,superdesk/superdesk-core,superdesk/superdesk-core,petrjasek/superdesk-core