Task: 29045
Story: 2004843
This patch pins pip to 18.1 as the latest pip 19.0 has a problem with
--no-cache-dir option. This problem is causing the build of docker
images of mariadb and kubeadm-aio to fail when they upgrade the
setuptools package.
Change-Id: If2b76249eeacec519a6a76605607ba6f3f81ac7d
Signed-off-by: Stamatis Katsaounis <mokats@intracom-telecom.com>