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.

Note that I didn't tackle reporting, which is still pretty rudimentary
for e2e.go. Now it looks like:

2014/12/08 15:32:58 Passed tests: [basic.sh basic.sh basic.sh certs.sh certs.sh certs.sh goe2e.sh goe2e.sh goe2e.sh guestbook.sh guestbook.sh guestbook.sh monitoring.sh monitoring.sh monitoring.sh pd.sh pd.sh pd.sh private.sh private.sh private.sh services.sh services.sh services.sh update.sh update.sh update.sh]
2014/12/08 15:32:58 Failed tests: []

Easy enough to post-process.
Looking at it further, this is actually pretty hideous. Yes, I can come up with a total ordering of the existing tests and check it in. That's fine. And we can actually demand that anyone adding tests do the same thing. It's actually a developer efficiency thing, though - if you add yet another stupid table, it's a point of friction you have to deal with every time you're adding a test, when it should be the responsibility of the consumer just to consume test names and results and not some positional argle-bargle.

I wish there was a format there was closer to jUnit, but more YAML-like, yet consumable in Jenkins. JUnit is consumable in Jenkins, but it's gross and not terribly human readable, which is a huge advantage of TAP. WTF test frameworks. I want something (a) vaguely human readable, and (b) not broken.