service_contexts

This allows wificond to publish binder interface using
service manager.

Denial warnings:

wificond: type=1400 audit(0.0:8): avc:
denied { call } for scontext=u:r:wificond:s0
tcontext=u:r:servicemanager:s0 tclass=binder permissive=1

wificond: type=1400 audit(0.0:9): avc:
denied { transfer } for scontext=u:r:wificond:s0
tcontext=u:r:servicemanager:s0 tclass=binder permissive=1

servicemanager: type=1400
audit(0.0:10): avc: denied { search } for name="6085" dev="proc"
ino=40626 scontext=u:r:servicemanager:s0 tcontext=u:r:wificond:s0
tclass=dir permissive=1

servicemanager: type=1400
audit(0.0:11): avc: denied { read } for name="current" dev="proc"
ino=40641 scontext=u:r:servicemanager:s0 tcontext=u:r:wificond:s0
tclass=file permissive=1

servicemanager: type=1400
audit(0.0:12): avc: denied { open } for path="/proc/6085/attr/current"
dev="proc" ino=40641 scontext=u:r:servicemanager:s0
tcontext=u:r:wificond:s0 tclass=file permissive=1

servicemanager: type=1400
audit(0.0:13): avc: denied { getattr } for
scontext=u:r:servicemanager:s0 tcontext=u:r:wificond:s0 tclass=process
permissive=1

SELinux : avc:  denied  { add } for
service=wificond pid=6085 uid=0 scontext=u:r:wificond:s0
tcontext=u:object_r:wifi_service:s0 tclass=service_manager permissive=1

BUG=28867093
TEST=compile
TEST=use a client to call wificond service through binder

Change-Id: I9312892caff171f17b04c30a415c07036b39ea7f