Fix pip installation

We don't need to have pip installed with easy_install because virtualenv
will install their own pip locally.

Change-Id: I1d469a685e59447bc2cad78031eeabd8f4fcd617
Closes-Bug: 1797931

roles/validate-tempest/tasks/pre-tempest.yml

@@ -52,12 +52,6 @@
   package: name=python-stestr state=present
   when: tempest_format in ['container', 'packages'] and release not in ['newton', 'ocata']
 
-- name: Install pip
-  easy_install:
-    name: pip
-    state: present
-  become: true
-
 - ignore_errors: true
   block:
     - name: Copying bugcheck files