Arcyd: put tryloop exceptions on main dashboard

Display try loop exceptions prominently on the main dashboard so that
it's obvious why Arcyd appears to have paused.

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/acceptance_tests.sh
$ ./testbed/arcyd/loop_test.sh
$ ./testbed/arcyd/status_html_testbed.sh

$ ./testbed/arcyd/test_shell.sh
  $ rm -rf ../origin
  observe the tryloop exception on the dashboard