Add TestApi to block the RollbackManagerHandlerThread.

To eliminate flakiness when testing timeout conditions for
RollbackTest.testEnableRollbackTimeoutFailsRollback.

Test: atest RollbackTest.testEnableRollbackTimeoutFailsRollback in a loop
Bug: 134373106
Change-Id: I2d1de148a83231f3fd48cc05b7320fa5fdf091ce
Merged-In: I01f3e769711ffa51fa714ff4bc81e70887f427ad
5 files changed