buildbot: send sigterm instead of sigkill to child

Because if e.g. 'devcam test' is the current child process, we want it to be
able to catch the signal and kill its own child too.

Change-Id: I3e3c9c10c8d7f5d793c98b604baf8df56608003e
Merge "buildbot: send sigterm instead of sigkill to child"
react: Add a better package comment

Change-Id: I427bcc0e8554323def325bf2d15707963299e45e