Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Fix kubelet flags.

pflag now sets golang flag `Parsed` before parsing flags https://github.com/spf13/pflag/commit/1ce0cc6db4029d97571db82f85092fccedb572ce. With that, all kubelet flags setting will be skipped.

We initially added `flag.Parsed` check to work around a issue that flags are parsed twice, thus kubelet flags are appended twice.

However, it doesn't seem to be the case now. I removed the `Parsed` check, and kubelet flags are only appended once.
```
/tmp/node-e2e-20180416T200912/kubelet --kubeconfig /tmp/node-e2e-20180416T200912/kubeconfig --root-dir /var/lib/kubelet --v 4 --logtostderr --allow-privileged true --network-plugin=kubenet --cni-bin-dir /tmp/node-e2e-20180416T200912/cni/bin --cni-conf-dir /tmp/node-e2e-20180416T200912/cni/net.d --hostname-override test-cos-beta-66-10452-53-0 --container-runtime docker --container-runtime-endpoint unix:///var/run/dockershim.sock --config /tmp/node-e2e-20180416T200912/kubelet-config --experimental-mounter-path=/tmp/node-e2e-20180416T200912/mounter --experimental-kernel-memcg-notification=true --runtime-cgroups=/system.slice/docker.service
```

This PR removes the unnecessary `Parsed` check to fix the test. @mtaufen 

/cc @kubernetes/sig-node-pr-reviews 
Signed-off-by: Lantao Liu <lantaol@google.com>

**Release note**:

```release-note
none
```