Reduce mini dfs logging verbosity.

Currently, the default log level is set to DEBUG. This produces approximately 10-20 GB of
logs per build, which is unacceptable.

Change-Id: Ibbb48876fc72faa23d76f32166f31f0257a7a3a0
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2386
Reviewed-by: Ishaan Joshi <ishaan@cloudera.com>
Reviewed-by: Casey Ching <casey@cloudera.com>
Tested-by: jenkins