Try to ensure tests run sequentially

Asynchronous operations that are performed in close() (such as
cleanupInternalState()) should complete before close() finishes.
Otherwise, we risk subsequent tests starting and causing racey
conditions while cleanup has not finished yet.

Fixes: 180192766
Test: atest CtsBiometricsTestCases
Test: atest com.android.server.biometrics
Change-Id: I3fdb3fe0be59e826d0c14e14a2590ccdde568774