Swith to coreos/go-log from ccding/go-logging

bump(github.com/coreos/go-etcd): 57864cf81c66b8605816fafab3ab142e1c5f5b29
bump(github.com/coreos/go-log/log):
bump(github.com/coreos/go-systemd): 52f153170a52158deffce83502a9b6aed3744802
Switch from golang log to coreos/go-log