* Support for Management Server Maintenance
- New APIs: prepareForMaintenance and cancelMaintenance, with required parameter - managementserverid.
- New management server states for maintenance: PreparingForMaintenance, Maintenance.
- listHosts API with optional parameter – managementserverid, to list the hosts connected to the management server.
- Support management server maintenance when more than one active management servers available.
- Triggers transfer agents to other available management servers for maintenance, new agent command MigrateAgentConnectionCommand to initiate transfer of indirect agents.
- New global config 'management.server.maintenance.timeout', to set the timeout (in mins) for the management server maintenance window, default: 60 mins.
- UI changes: Prepare and Cancel Maintenance in Management Server section, Connected Agents tab, New fields for hosts and management servers.
* Updated pending jobs check timer task with ScheduledExecutorService
* keep maintenance state on trigger shutdown call when ms is in maintenance
* add pending jobs count to ms response
* during ms heartbeat, update state to up only when it's down
* allow vm work jobs of async job created before prepare for maintenance
* Revert "keep maintenance state on trigger shutdown call when ms is in maintenance"
This reverts commit 607e13364679eac897f4d146bb3325ea7a61ba17.
* skip maintenance test when multiple management servers are not available, and not configured in host setting for kvm
