Cert: gracefully tear down real device test

* Send SIGINT to the backing process' actual PID on Android device
  instead of simply terminating the adb command
* Shorting the SIGINT timeout to 5 seconds and the SIGKILL timeout to 1
  second

Bug: 188945235
Tag: #gd-refactor
Test: gd/cert/run --device SimpleHalTest
Test: gd/cert/run SimpleHalTest
Change-Id: I66159324b7ee0d1e0838d473bc5e188bf669f4f8