Conditionally apply pip_lock_down role

This commit adds variable ``tempest_developer_mode`` and conditionally
applies pip_lock_down when ``tempest_developer_mode`` is false.  This
is necessary when installing tempest in a functional test.

By default, ``tempest_developer_mode`` will remain false so that the
default behaviour of the role is maintained.

Change-Id: I262fca0717520efb554ae83cb38d3b7f8d001abe

defaults/main.yml

@@ -22,6 +22,7 @@ verbose: True
 
 tempest_git_repo: https://git.openstack.org/openstack/tempest
 tempest_git_install_branch: master
+tempest_developer_mode: false
 
 tempest_venv_download_url: http://127.0.0.1/venvs/untagged/ubuntu/tempest.tgz
 tempest_fatal_deprecations: False

meta/main.yml

@@ -31,5 +31,10 @@ galaxy_info:
     - openstack
 dependencies:
   - apt_package_pinning
+  - role: pip_lock_down
+    when:
+      - not tempest_developer_mode | bool
+  - role: pip_install
+    when:
+      - tempest_developer_mode | bool
   - openstack_openrc
-  - pip_lock_down