New "selinux.restorecon" control property.

This new property is used as a control verb for running a recursive
restorecon at the path contained in the property value.

Defines a new label and grants access to vold, which invokes it when
mounting private adopted volumes.

Bug: 21121357
Change-Id: I8ff12a146e54a505aa5b43a542578891563d647a
diff --git a/property_contexts b/property_contexts
index 1844910..5bdb3c3 100644
--- a/property_contexts
+++ b/property_contexts
@@ -41,7 +41,8 @@
 persist.security.       u:object_r:system_prop:s0
 
 # selinux non-persistent properties
-selinux.                u:object_r:security_prop:s0
+selinux.restorecon_recursive   u:object_r:restorecon_prop:s0
+selinux.                       u:object_r:security_prop:s0
 
 # default property context
 *                       u:object_r:default_prop:s0