sepolicy :[2/2] fix system_file_type and get_prop for coredomians.

As part of new AOSP restriction all the domains which are working
from system partation should have "system_file_type" attribute
else will lead to compile time failure .
For reading / setting any property  we should be using
following macros .
set_prop( domain, property_label)
get_prop( domain, property_label)

So addressing  these as part of new requirments .
Change-Id: Ie7a9c72994f3a1a62f8cf70d40a3a56d494a1726