CBG-1391 Recover from concurrent cbgt index creation error (#4993)
CBG-1391 Recover from concurrent cbgt index creation error (#4993)

On cbgt index creation, SG retrieves the existing index UUID if present, and passes to cbgt for index creation/update.  During concurrent index creation by multiple SG nodes, a node can retrieve an empty UUID and subsequently hit an 'index already exists' error.  This should be treated as a non-fatal error, as SG will use the existing index.
couchbaselabs/sync_gateway,couchbaselabs/sync_gateway,couchbaselabs/sync_gateway,couchbaselabs/sync_gateway