use median instead of average
use 300 for default message_num, rostopic hz uses 50000? https://github.com/ros/ros_comm/blob/indigo-devel/tools/rostopic/src/rostopic/__init__.py#L111
Merge pull request #567 from k-okada/fix_to_pass_test

fix hz mesaure test
Merge branch 'master' of https://github.com/jsk-ros-pkg/jsk_common into set-android-path