Allow apps to execute ping

Addresses the following denials:

<5>[  170.166218] type=1400 audit(1386789488.029:57): avc:  denied  { getattr } for  pid=4352 comm="sh" path="/system/bin/ping" dev="mmcblk0p25" ino=182 scontext=u:r:untrusted_app:s0 tcontext=u:object_r:ping_exec:s0 tclass=file
<5>[  170.166356] type=1400 audit(1386789488.029:58): avc:  denied  { execute } for  pid=4352 comm="sh" name="ping" dev="mmcblk0p25" ino=182 scontext=u:r:untrusted_app:s0 tcontext=u:object_r:ping_exec:s0 tclass=file
<5>[  170.166841] type=1400 audit(1386789488.029:59): avc:  denied  { read open } for  pid=4389 comm="sh" name="ping" dev="mmcblk0p25" ino=182 scontext=u:r:untrusted_app:s0 tcontext=u:object_r:ping_exec:s0 tclass=file
<5>[  170.166962] type=1400 audit(1386789488.029:60): avc:  denied  { execute_no_trans } for  pid=4389 comm="sh" path="/system/bin/ping" dev="mmcblk0p25" ino=182 scontext=u:r:untrusted_app:s0 tcontext=u:object_r:ping_exec:s0 tclass=file

Change-Id: Ic175ef7392897a3941c36db67dfa59ded35204b5