selinux: grant rx perms to toolbox_exec where needed

AOSP commit a3c97a7660ba ("Only allow toolbox exec where /system
exec was already allowed.") removed domain's rx perms to
toolbox_exec. This breaks a number of domains on bullhead. Restore
rx perms for toolbox_exec where needed.

Bug: 24341811
Change-Id: I991c66a9746a4b29f454cb7a1b5e7ba1180ed94f
3 files changed