Kill commands that outlive test env

There is a timeout on the test env worker, once it is passed the gearman
job is cancelled. If this occurs and testenv-client is waiting for the
thread running the command to complete, we kill everything in the process
group.

Change-Id: I629fdd8f17bc95274dbad11465b2653514dc5e7c
Set the worker timeout

Use the value for DEVSTACK_GATE_TIMEOUT to set the worker timeout of the
test environment.

Change-Id: I68f0cb8e1852270f70639063e463a25eb4d969e0
Merge "Kill commands that outlive test env"
Merge "Set the worker timeout"