Activate virtualenv for model generation

In the cookiecutter-templates/requirements.txt
is used a requirement from pull request on github.com.
Pip 8.1.1 which is installed on cfg01 by default, cannot
correctly checkout the pull request.

- Create and activate virtualenv in the
  MACRO_GENERATE_COOKIECUTTER_MODEL()
- Update pip to the latest version

Change-Id: I9e802983c42671986ba835a74aac6114298abb65
1 file changed