GdCert: Split GdDevice into Host and Android and improve teardown method

* Split GdDevice class into GdHostOnlyDevice and GdAndroidDevice
* Create setup() and teardown() method for GdDeviceBase as life cycle
  methods
* In teardown(), wait for SIGINT termination with a finite timeout,
  if SIGINT failed to stop the backing process in time, try sending
  SIGKILL instead. All in all, we need to make sure that the backing
  process is completely stopped in time when the GdDeviceBase class
  is asked to teardown

Test: gd/cert/run for both host and device based tests
Bug: 153274925
Bug: 153275907
Change-Id: I6ccd037dd0f2493c07788c6f454750e3f69e7761