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 angler. Restore
rx perms for toolbox_exec where needed.

Bug: 24341811
Change-Id: I9abf786ffa8f948870b17cf0dcf38e166fa6926b
3 files changed