Install pip

Pip isn't installed on undercloud, making Install stackviz task fails
because isn't able to find it.

Change-Id: I3aac9a91e1ca74f03d84694239b0a8299dfc9c85

roles/validate-tempest/tasks/stackviz.yml

@@ -8,6 +8,12 @@
       dest: "{{ working_dir }}/stackviz_static"
       use_ssh_args: true
 
+- name: Install pip
+  easy_install:
+    name: pip
+    state: present
+  become: true
+
 - name: Install stackviz
   pip:
     name: "."