A common source of mistakes when authoring sepolicy is properly
setting up property sets. This is a 3 part step of:
1. Allowing the unix domain connection to the init/property service
2. Allowing write on the property_socket file
3. Allowing the set on class property_service

The macro unix_socket_connect() handled 1 and 2, but could be
confusing for first time policy authors. 3 had to be explicitly
added.

To correct this, we introduce a new macros:
set_prop(sourcedomain, targetprop)

This macro handles steps 1, 2 and 3.

No difference in sediff is expected.

Change-Id: I630ba0178439c935d08062892990d43a3cc1239e
Signed-off-by: William Roberts <william.c.roberts@linux.intel.com>