Enable more test cases for serial execution mode in SharedArbitratorT…

…est (#10916)

Summary:
As title, and with minor refactors.

The following 3 cases will still be executed with parallel mode only because:

1. `asyncArbitratonFromNonDriverContext`: Plan doesn't support serial execution
2. `arbitrateMemoryFromOtherOperator`: Plan doesn't support serial execution
3. `concurrentArbitration`: Test run hangs

`3` should be fixed in subsequent PR.

Pull Request resolved: #10916

Reviewed By: bikramSingh91

Differential Revision: D62169461

Pulled By: xiaoxmeng

fbshipit-source-id: c506f9d73d8d663abfb2d79fb0bbbcc0eb5bd9b9