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.
Yup. I'd like to work with you on the Jenkins side. I have a TAP parser installed so I can double check output, but all that's going to do is prove conformance and not usefulness within the plugin. (I also want e2e.go output to actually stay useful and log what's doing along the way, but in a TAP happy way, which is why it's going to take a little bit more effort. Otherwise this wouldn't take that long.)

It looks like the convention might be to label the test after the number, so it's possible consumers might infer correlations past that. I've never worked with a TAP consumer, though.

Ideally we'd dovetail this work and the integration tests, too, if we're going through this effort. I'll look into what that even looks like.