Switch file_contexts to use label-by-link support.
Switch file_contexts to use label-by-link support.

Depends on changes to external/libselinux and system/core
with the same Change-Id.

Change-Id: Id6c2597eee2b6723a5089dcf7c450f8d0a4128f4
Signed-off-by: Stephen Smalley <d6e1285e1c84d3d5885c2124fdacc780e9fc0a94@tycho.nsa.gov>

maruos/android_device_lge_hammerhead,maruos/android_device_lge_hammerhead,maruos/android_device_lge_hammerhead,maruos/android_device_lge_hammerhead