Description of problem:

The 'kubectl exec' command has regressed, and produces this failure:

error: error executing remote command: Error executing command in container: Unrecognized input header

Version-Release number of selected component (if applicable):

# rpm -q kubernetes
kubernetes-1.2.0-0.4.alpha1.git4c8e6f4.fc23.x86_64

How reproducible:

Every time

Steps to Reproduce:
1. Run some pods.
2. Run the code below.

Actual results:

# rpm -q kubernetes
kubernetes-1.2.0-0.4.alpha1.git4c8e6f4.fc23.x86_64
# rpm -q docker
docker-1.10.2-1.git86e59a5.fc23.x86_64
# docker exec k8s_mock-container.88f1f36_mock-aogwd_default_d53a657a-db98-11e5-8811-9e005dd50001_39e4050e date
Thu Feb 25 08:39:58 UTC 2016
# kubectl get pods
NAME         READY     STATUS    RESTARTS   AGE
mock-aogwd   1/1       Running   0          2m
mock-cxirx   1/1       Running   0          2m
# kubectl exec mock-aogwd -- date
error: error executing remote command: Error executing command in container: Unrecognized input header

Expected results:

# rpm -q kubernetes
kubernetes-1.1.0-0.17.git388061f.fc23.x86_64
# rpm -q docker
docker-1.9.1-6.git6ec29ef.fc23.x86_64
# kubectl get pods
NAME         READY     STATUS    RESTARTS   AGE
mock-on1bw   1/1       Running   0          46s
mock-ra9ad   1/1       Running   0          36s
# kubectl exec mock-on1bw -- date
Thu Feb 25 08:36:13 UTC 2016