Quick submission of drivers in tests to mesos scheduler results in dropping drivers

Queued drivers in MesosClusterScheduler are ordered based on MesosDriverDescription - and the default ordering checks for priority, followed by submission time. For two driver submissions with same priority and if made in quick succession (such that submission time is same due to millisecond granularity of Date), this results in dropping the second MesosDriverDescription from the queuedDrivers - as driverOrdering returns 0 when comparing the descriptions. This jira fixes the more immediate issue with tests, but we do need to relook at this for mess scheduler in general later.

Currently, this affects tests - for example, in the latest VOTE for 3.3.1 [1] - and is not consistently reproducible unless on a fast machine.

[1] https://lists.apache.org/thread/jof098qxp0s6qqmt9qwv52f9665b1pjg