add virtualenv role

roles/virtualenv/README.rst

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+This roles allows to create a Python virtual environment.
+
+The role should be used with the following parameters:
+
+``venv_user``
+    The user under which the virtual environment is created
+
+``venv_home_dir``
+    ansible likes absolute paths in way too many places, the virtual
+    environment is created in the users' home directory and this is its path
+
+``venv_name``
+    The name of the virtual environment
+
+``venv_packages``
+    packages to be installed using 'pkgng'
+
+``venv_python_packages``
+    Python packages to be installed using 'pip install'

roles/virtualenv/tasks/main.yml

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+---
+# This is mostly for pysqlite that needs to find locally installed sqlite3
+# headers and libraries.  But it might be needed for other modules as well.
+- name: prepare ~/.pydistutils.cfg
+  ini_file:
+    dest: "{{ venv_home_dir }}/.pydistutils.cfg"
+    section: "build_ext"
+    option: "{{ item.option }}"
+    value: "{{ item.value }}"
+    owner: "{{ venv_user }}"
+  with_items:
+  - option: include_dirs
+    value: "/usr/local/include"
+  - option: library_dirs
+    value: "/usr/local/lib"
+
+- name: install system packages
+  pkgng:
+    name: "{{item}}"
+    state: present
+  with_items: venv_packages
+
+- name: create the virtual environment
+  sudo_user: "{{ venv_user }}"
+  pip:
+    name: "{{ item }}"
+    virtualenv: "{{ venv_home_dir }}/{{ venv_name }}"
+  with_items: venv_python_packages