Cert: make test setup more robust to binary failures

* Add checks to see if a backing process or root-canal is alive
  immediately after launching them to avoid making the whole
  test stuck on a response from these dead processes
* Add methods to disable verity on test devices and push test files
  to required directories on the Android device

Bug: 150321998
Test: source gd/cert/set_up_and_run_device_cert.sh
Change-Id: I44f2e73aa88e7924c7e594faad020f8199c76994