Move flaky HIDL VHAL impl test to post submit.

The tests is flaky by nature because it depends on timer. Although
the flakiness is low, it is too flaky to run as presubmit.

Test: atest -s emulator-5554 DefaultVhalImplTest
Bug: 288197123
Change-Id: I735e3e6197769e47372f025d7eb82d54159a8ff8