GdCert: Kill root-canal process if SIGINT failed

* Wait for 10 seconds after sending SIGINT to root-canal
* If that doesn't work, send SIGKILL and wait for 10 seconds

Bug: 153274925
Bug: 153275907
Test: gd/cert/run --host
Change-Id: Id62bc95fe30a6b3a6b552b479d85e9a4ed755978