Add --times to e2e.go

Make each test available for execution --times times. Acts like a
multi-deck shoe. (Otherwise this is easily scriptable outside the
e2e.go command).

Useful for "I want to walk away for a few hours leaving some end-to-ends
running", until we have more stress tests. Also useful for detecting
flakes.

Reporting is changed to break out Passed, Flaky and Failed. I chose to
keep all three lines even if --times isn't on, just for consistency in
scraping. Similarly, it always outputs the counts now. A report looks
like:

2014/12/09 07:31:21 Passed tests: goe2e.sh[100/100] guestbook.sh[100/100] private.sh[100/100] services.sh[100/100]
2014/12/09 07:31:21 Flaky tests: basic.sh[99/100] certs.sh[99/100] monitoring.sh[98/100] pd.sh[98/100] update.sh[98/100]
2014/12/09 07:31:21 Failed tests:
2014/12/09 07:31:21 8 test(s) failed.