Don't use easy_install on Ubuntu 18+

Currently easy_install is not available on Ubuntu 18+ due to [1]. In
that case, install pip via apt rather than easy_install.

[1]
https://bugs.launchpad.net/ubuntu/+source/python-setuptools/+bug/1774419

Change-Id: Id358fdb655d71490b0915680dff131cfe33f4a40
Closes-Bug: #1813492

ansible/roles/baremetal/defaults/main.yml

@@ -68,9 +68,16 @@ docker_custom_option: ""
 
 docker_runtime_directory: ""
 
+# Ubuntu 18+ does not have easy_install available due to
+# https://bugs.launchpad.net/ubuntu/+source/python-setuptools/+bug/1774419.
+easy_install_available: >-
+  {{ ansible_distribution != 'Ubuntu' or
+     ansible_distribution_major_version is version(18, 'lt') }}
+
 debian_pkg_install:
  - "{{ docker_apt_package }}"
  - git
+ - "{% if not easy_install_available %}python-pip{% endif %}"
  - python-setuptools
  - ntp
 

ansible/roles/baremetal/tasks/install.yml

@@ -108,6 +108,7 @@
     virtualenv: "{{ virtualenv is none | ternary(omit, virtualenv) }}"
     virtualenv_site_packages: "{{ virtualenv is none | ternary(omit, virtualenv_site_packages) }}"
   become: True
+  when: easy_install_available
 
 - name: Install latest pip in the virtualenv
   pip: