property_service: log pid,uid and gid of setprop client

When auditing setprop denials, it is often unclear of who the process is
in a multi-process domain. To help identify the invoker, log the pid, uid,
and gid of the caller.

Before:
avc:  denied  { set } for property=wifi.xxx ...

After:
avc:  denied  { set } for property=wifi.xxx pid=30691 uid=123 gid=345 ...

Change-Id: I5cdcb3d18fbd52e0987b5e1497b9f6620c6c742a
Signed-off-by: William Roberts <william.c.roberts@intel.com>