Installs virtual environment

def install_virtualenv(parser_args):
    """ Installs virtual environment """
    python_version = '.'.join(str(v) for v in sys.version_info[:2])
    sys.stdout.write('Installing Python {0} virtualenv into {1} \n'.format(python_version, VE_ROOT))
    if sys.version_info < (3, 3):
        install_virtualenv_p2(VE_ROOT, python_version)
    else:
        install_virtualenv_p3(VE_ROOT, python_version)