KeyMint: make test more robust to variations

Only perform the population of a fake module hash if the keystore2
flag is off (indicating that the real module hash will not be populated)

Also hold off from running the test until Keystore has done the
population, so tests that rely on the module hash being populated
are more likely to work.

Bug: 369375199
Bug: 380020528
Test: VtsAidlKeyMintTargetTest
Change-Id: Ib4978349c70427065a004db775a13311d1bf4754