Drop VLOG level passed into Kudu client

I'm running a concurrent stress workload with lots of small queries. By changing the impalad vlog level from 1 to 0, my QPS went from ~17qps to around 60qps.

We should consider passing FLAGS_v - 1 into Kudu's vlog level, since we generally assume that VLOG=1 is allowed to be relatively noisy (eg logging thread start/stop, etc) whereas it seems like Impala's policy is that VLOG(1) should be fairly quiet.