Use bob_dbmanage.py installed on the virtualenv

gitlab/before_test.sh

@@ -26,6 +26,6 @@ fi
 run_cmd ${use_pip} install --upgrade --use-wheel --no-index --pre dist/*.whl
 
 # Downloads databases that may be missing (not shipped with python pkg)
-if [ -x ./bin/bob_dbmanage.py ]; then
-  run_cmd ./bin/bob_dbmanage.py all download --missing;
+if [ -x ${PREFIX}/bin/bob_dbmanage.py ]; then
+  run_cmd ${PREFIX}/bin/bob_dbmanage.py all download --missing;
 fi