Faster update

[carlpaten]

I would like to run bin/update-plugins all in my login script, but it slows things down significantly - it usually takes 2-3 seconds for it to run. I only have 3 plug-ins.

It would be nice if tpm update-plugins took <1 second to run in the general case.

strace -c says that the vast majority of the time is spent on three wait4 calls, including one which errors out.