arcyd/test_shell: log git http server out to file
arcyd/test_shell.sh: add 'kill' and 'start'

Make it easier to test arcyd restarts by supplying 'kill' and 'start'
scripts so it's easily possible to bounce it.

Test Plan:
$ ./testbed/arcyd/test_shell.sh
$ ./kill_arcyd.sh
$ ./start_arcyd.sh
Arcyd: reduce restart time by caching urlwatcher

Restart time has grown too much, reduce it by dumping the state of the
phlsys_urlwatcher and loading it on startup.

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/acceptance_tests.sh
$ ./testbed/arcyd/test_shell.sh
  .. create new review while arcyd is down ..