Create virtualenv without downloading

When creating the virtualenv, we would rather just
use the pip/setuptools packages already available on
the host, then upgrade them later. This helps keeps
the builds isolated to the versions we want, and
reduces outgoing requests which is important for
isolated builds.

Change-Id: Iba22f5a11af858b52f006494b30002d34e5aa4f6

defaults/main.yml

@@ -104,6 +104,7 @@ repo_build_venv_pip_install_options: >-
 repo_build_venv_command_options: >-
   {{ virtualenv_bin }}
   {{ (ansible_pkg_mgr == 'apt') | ternary('--always-copy', '') }}
+  --no-download
 
 # Path to the repo build venv binaries
 repo_build_bin: "/openstack/venvs/repo-build-{{ repo_build_release_tag }}/bin"