turn off verbose jetty logging in tests

verbose jetty logging inflates test results about 4M per run, and
the verbosity is pretty boring and useless in normal testing.

(I had earlier turned it on to try to catch a specific rare flakiness,
but it wasn't helpful.)

[felix8a, 2013-09-12 23:44:38]

ping

[ihab.awad, 2013-09-19 17:40:26]

lgtm

[felix8a, 2013-09-19 20:14:12]

@r5599