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.

Shifts both SELinux actions to occur before the actual property set
occurs, so setters can watch for completion.

Bug: 21121357
Change-Id: I3db3eb876ae66e144b3bfd648349b66a028511fd