Update OTA to understand SELinux labels and capabilities

Update the OTA generation script to understand SELinux file
labels and file capabilities.

Make fs_config aware of SELinux labels and file capabilities, and
optionally output those elements whenever we output the
UID / GID / file perms. The information is emitted as a key=value pair
to allow for future extensibility.

Pass the SELinux file label and capabilities to the newly created
set_metadata() and set_metadata_recursive() calls. When the OTA
script fixes up filesystem permissions, it will also fix up the SELinux
labels and file capabilities.

If no SELinux label and capabilities are available for the file, use
the old set_perm and set_perm_recursive calls.

Bug: 8985290
Bug: 10183961
Bug: 10186213
Change-Id: I4fcfb2c234dbfb965cee9e62f060092a4274d22d