Install pip when not using a kayobe target virtualenv

Previously we were relying on kolla-ansible's baremetal role to install pip, but if
virtualenvs are used for the target hosts with kolla-ansible (but not kayobe), then
pip will not be installed to the system site packages. This change installs pip
using easy_install if target virtualenvs are not in use for kayobe.

ansible/kayobe-target-venv.yml

@@ -52,3 +52,9 @@
           vars:
             activate_virtualenv_path: "{{ virtualenv }}"
       when: virtualenv is defined
+
+    - name: Ensure pip is installed
+      easy_install:
+        name: pip
+      become: True
+      when: virtualenv is not defined