Do not allow new additions to core_property_type

core_property_type is an attribute which was given to all existing
properties known to core SELinux policy. Any property with this label is
readable to all SELinux domains, which is overly broad. The long term
goal is to remove the core_property_type attribute entirely.

Add a neverallow rule prohibiting the introduction of new properties
with the core_property_type attribute. Device specific properties, or
new properties in core SELinux policy, should not have this attribute.

Test: policy compiles
Change-Id: Ie89a9f0d81c8561616001ff8451496ce2278dbb2