Adds caller check to getAllPackages()

This change enforces that only system, root or shell may call
getAllPackages(), a hidden API that shares all package names regardless
of user, instant app or package visibility rules.

The only exception is the uid of iorapd. iorapd needs the package info
to prefetch the right data.

Bug: 179618216
Bug: 174661955
Test: run iorapd and check it works well.
Change-Id: I77460ae19a4d41151577646441f11e2eddbb741a