Change ExecUtils to support callbacks.

artd needs the callbacks to get the pid in order to kill the subprocess.

Bug: 244412198
Test: m test-art-host-gtest-art_runtime_tests
Ignore-AOSP-First: Will cherry-pick later.
Change-Id: I8c40949b5ed88ff85ddedad9d86f0b9bbfddb98d
5 files changed