Don't require --debugfs and --tmpdir when --flattened is used.

Also fix runtests.sh to not build debugfs when testing a flattened APEX.

Test: art/build/apex/runtests.sh (ignoring libziparchive failure due to b/138103882)
Test: art/build/apex/art_apex_test.py --flattened \
  --debug out/target/product/taimen/system/apex/com.android.runtime.debug
Bug: 135535106

Change-Id: Id1b56646c28587c7dfb4a2f140706f2d29c8dfb3
2 files changed