Mark nodes as 'in-use' before launching jobs

While we immediately lock a node given to us by nodepool, we delay
setting the node to 'in-use' until we actually request that the job
be launched so that if we end up canceling the job before it is
run, we might return the node unused to nodepool.

Change-Id: I2d2c0f9cdb4c199f2ed309e7b0cfc62e071037fa
5 files changed