Use import for test-mapping rather than requesting files remain in sync

If there were intervening parent directories with extra TEST_MAPPING
files, then "imports" might pick up extra modules, but in this case that
won't happen.
This change will ensure these two TEST_MAPPING file remain in sync.

Test: atest -p frameworks/base/tools/hoststubgen:ravenwood-presubmit --dry-run
	Finding Tests...
	Found 'RavenwoodBivalentTest' as MODULE
	Found 'RavenwoodMockitoTest' as MODULE
	Found 'RavenwoodMinimumTest' as MODULE
	Found 'RavenwoodCoreTest' as MODULE
	Found 'CtsUtilTestCasesRavenwood' as MODULE
Change-Id: I89d308e1596fa689aeb3c2e476c7707c0ff4dd8f