Don't fial if virtualenv is not installed and we do not need to initialize the virtualenv

Fixes #688

lib/ansible/modules/packaging/language/pip.py

@@ -98,7 +98,7 @@ options:
     required: false
     default: null
 notes:
-   - Please note that virtualenv (U(http://www.virtualenv.org/)) must be installed on the remote host if the virtualenv parameter is specified.
+   - Please note that virtualenv (U(http://www.virtualenv.org/)) must be installed on the remote host if the virtualenv parameter is specified and the virtualenv needs to be initialized.
 requirements: [ "virtualenv", "pip" ]
 author: Matt Wright
 '''
@@ -252,12 +252,14 @@ def main():
 
     if env:
         env = os.path.expanduser(env)
-        virtualenv = os.path.expanduser(virtualenv_command)
-        if os.path.basename(virtualenv) == virtualenv:
-            virtualenv = module.get_bin_path(virtualenv_command, True)
         if not os.path.exists(os.path.join(env, 'bin', 'activate')):
             if module.check_mode:
                 module.exit_json(changed=True)
+
+            virtualenv = os.path.expanduser(virtualenv_command)
+            if os.path.basename(virtualenv) == virtualenv:
+                virtualenv = module.get_bin_path(virtualenv_command, True)
+
             if module.params['virtualenv_site_packages']:
                 cmd = '%s --system-site-packages %s' % (virtualenv, env)
             else: