Adding profiling support to servenv, zkclient2.

And the test now collects pprof info.
Just run:
./zkocc_test.py -v TestZkocc.test_vtgate_qps --skip-teardown
Then run:
go tool pprof $VTROOT/bin/vtgate $VTDATAROOT/tmp/vtgate.pprof
(or with zkclient2 for the client side)
and for instance type 'web' in the prompt.
Adding comment to test.