Don't use apexName where apexBundleName is expected

With I63f8a1de463011c6e0b97f5f6eee83103e22bc30, a flattened APEX is
installed to /system/apex/<apexBundleName> not /system/apex/<apexName>.
The change was to be in sync with the non-flattened APEXes that are
installed to /system/apex/<apexBundleName>.apex.

apexName is from the 'name' property while apexBundleName is from the
'apex_name' property. The two names are mostly the same, but can be
different, notably for the ART and the VNDK APEXes. e,g apexName =
com.android.art, apexBundleName = com.android.art.release.

However, there was a bug in the fix; we haven't updated the path for the
flattened APEXes in other places: filecontexts and symlinks. As a
result, the files for the APEXes where apexName is different from
apexBundleName were incorrectly labeled and caused a boot loop.

Fixing the bug.

Bug: 140136207
Bug: 149013536
Test: m
Test: OVERRIDE_TARGET_FLATTEN_APEX=true m; then inspect the built
system.img to verify that
/system/apex/com.android.vndk.current/lib/libcrypto.so is correctly
labeled as system_lib_file.

Change-Id: I4aaf674a5daeabab5ed6e7025c5389821ee9a013