Fix: a module with sub_dir can't be placed in APEX

This change fixes the bug that when a module is defined with sub_dir,
then build breaks when the module is included in an APEX.

This was happening because, for example when we have a prebuilt_etc
module having sub_dir set to "foo/bar", then only etc/foo/bar is added
to the canned_fs_config file and other intermediate directories (etc,
etc/foo) are not added. e2fsdroid however expects that every directories
to be listed.

Fixing the problem by adding parent directories when adding a directory
to canned_fs_config.

Bug: 120600179
Test: m (a new test case added to apex_test)
Change-Id: If712ff65761a7e1e3216371bb2eb7acf9cb5dc9e