Install python-minimal for Xenial

Xenial images by default don't come with python2 installed.
Unfortunately ansible requires python2 on the host to run (for now,
though [1] is in preview).  In the mean time, ensure we have
python-minimal.

I think that under standard conditions, this is being dragged in by
other dependencies anyway.  The place I noticed was launching a
vexxhost control-plane node, using their Xenial base images.

[1] https://docs.ansible.com/ansible/python_3_support.html

Change-Id: I0e4020e9b8407271c88c3c5ac332393f6dd28418

install_puppet.sh

@@ -203,6 +203,11 @@ EOF
         fi
         dpkg -i $puppet_deb
         rm $puppet_deb
+
+        # ansible also requires python2 on the host to run correctly.
+        # Make sure we have it, as some images come without it
+        DEBIAN_FRONTEND=noninteractive apt-get --option 'Dpkg::Options::=--force-confold' \
+            --assume-yes install python-minimal
     fi;
 
     apt-get update