Fix FetchNextJob inter srvs race condition
Fix FetchNextJob inter srvs race condition

To ease race condition over the locking of the fetch/read idx, when large number of srvs attempt to fetch the same job. 
This situation occurred in AWS env, with high connect/'walk around' times to DC memcache srv
kaltura/server,kaltura/server,kaltura/server,kaltura/server,kaltura/server,kaltura/server