Addresses transient failures in the following test classes:
* ITestAbfsStreamStatistics: Uses a filesystem level static instance to record read/write statistics, which also tracks these operations in other tests running in parallel. Marked for sequential-only run to avoid transient failure
* ITestAbfsRestOperationException: The use of a static member to track retry count causes transient failures when two tests of this class happen to run together. Switch to non-static variable for assertions on retry count
closes#3341
Contributed by Sumangala Patki
82658a22d6