Handle race conditions in the quota management implementation

[z103cb]

The current implementation of the type QuotaManagerInterface interface { instantiated at unc NewQuotaManager(dispatchedAWDemands map[string]*clusterstateapi.Resource, dispatchedAWs map[string]*arbv1.AppWrapper, is being accessed concurrently from multiple threads.

The points in which the QuotaManager is being accessed are:

• Cleanup function. Cleanup is called by the manageQueueJob function, called by the worker function running in a daemon thread.
• In the ScheduleNext function if fits, preemptAWs, _ := qjm.quotaManager.Fits(qj, qjAggrResources, proposedPreemptions); fits {, which runs in a demon go routine.

[z103cb]

@tardieu I believe that this issue should be prioritised high.

[z103cb]

This issue has been resolved by merging #367