Arcyd: richer stats on the dashboard

Make it easier to see what's taking time in an Arcyd instance by
providing a richer set of statistics based on time taken per cycle.

Display min, mean, max, last, count in addition to existing values.

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

Observe output from:
$ ./testbed/arcyd/status_html_testbed.sh
$ ./testbed/arcyd/loop_test.sh