goldfish_setup: grant /system/bin/sh exec access

The goldfish_setup shell script needs the ability to execute
the shell script interpreter. Allow it.

Addresses the following denial:

avc: denied { getattr } for pid=1220 comm="init.goldfish.s"
path="/system/bin/sh" dev="vda" ino=442 scontext=u:r:goldfish_setup:s0
tcontext=u:object_r:shell_exec:s0 tclass=file permissive=0

Bug: 28941573
Change-Id: I22d26e90f107c8d801229354a5e0513c37e6c31d