[Bug 1274854] kubectl exec: handshake did not verify certificate chain

[Red Hat Bugzilla]

https://bugzilla.redhat.com/show_bug.cgi?id=1274854

--- Comment #8 from Jan Chaloupka  ---
backported code from 1.2.0:

http://pkgs.fedoraproject.org/cgit/kubernetes.git/commit/?h=f23&id=b0821...