fix: install in a .venv artifact

This artifact can be reused in different stages.

ref: N25B-367

.gitlab-ci.yml

@@ -21,6 +21,9 @@ install:
   tags:
     - install
   script:
+    - python -m virtualenv .venv
+    - source .venv/bin/activate
+    - echo /qi/pynaoqi-python2.7-2.5.7.1-linux64/lib/python2.7/site-packages/ > .venv/lib/python2.7/site-packages/pynaoqi-python2.7.pth
     - pip install -r requirements.txt
   artifacts:
     paths:
@@ -35,4 +38,5 @@ test:
   tags:
     - test
   script:
-    - PYTHONPATH=${PYTHONPATH}:src pytest test/
+    - source .venv/bin/activate
+    - PYTHONPATH=src pytest test/