trying to copy it via NFS.

Add code to restart the tmcc proxy, which appears to die off for no
apparent reason. I now waitpid for it while the jail is running, and
restart if it exits.

At Mike's suggestion temporarily wrap tmcc proxy in a ktrace to see if we
can debug this problem. The ktrace file (using -a option) is written as
/var/emulab/jails/nodeid/tmcc.ktrace.