Gate: update paths for pip 10 installation

Pip>=10 moves the entrypoint to /usr/local/bin from /usr/bin, this
ps forces the shell to forget all locations following upgrade
to allow it to adapt to the new location.

Change-Id: I1ed92b75f689e982397cd4fc87ac262256e161e8

tools/images/kubeadm-aio/Dockerfile

@@ -55,6 +55,7 @@ RUN set -ex ;\
         python-pip \
         gawk ;\
     pip --no-cache-dir install --upgrade pip ;\
+    hash -r ;\
     pip --no-cache-dir install setuptools ;\
     pip --no-cache-dir install kubernetes ;\
     pip --no-cache-dir install ansible ;\