library/roles/python-env: Fix the variables handling

python-env/defaults/main.yml

@@ -5,7 +5,10 @@ py_env_basic_pkgs:
   - python-pip
 
 py_env_dpkg:
+  -
 
 py_pip_deps:
+  -
 
 py_env_pip_pkgs:
+  -

python-env/tasks/main.yml

@@ -14,7 +14,7 @@
       with_items: '{{ py_pip_deps | default([]) }}'
 
     - name: Install a list of pip packages
-      pip: name={{ item }} virtualenv={{ py_env_env_base_dir }}
-      with_items: '{{ py_env_pip_pkgs | default ()[] }}'
+      pip: name={{ item }}
+      with_items: '{{ py_env_pip_pkgs | default ([]) }}'
 
   tags: [ "python", "py_env" ]