Allow domains to stat and open their entrypoint executables.

Resolves denials such as:
 avc:  denied  { open } for  pid=2758 comm="mediaserver" name="mediaserver" dev="mmcblk0p22" ino=169 scontext=u:r:mediaserver:s0 tcontext=u:object_r:mediaserver_exec:s0 tclass=file
 avc:  denied  { getattr } for  pid=2758 comm="mediaserver" path="/system/bin/mediaserver" dev="mmcblk0p22" ino=169 scontext=u:r:mediaserver:s0 tcontext=u:object_r:mediaserver_exec:s0 tclass=file

Change-Id: Ifee9e6fa87ae933639ce0b1d69a2feee460cf31f
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>