mongodb_user: fix ssl_cert_reqs exception (#2573)

If ssl is not enabled, but ssl_cert_reqs is passed to pymongo, an
exception occures.

Fixes: #2571

lib/ansible/modules/extras/database/misc/mongodb_user.py

@@ -299,7 +299,9 @@ def main():
     user = module.params['name']
     password = module.params['password']
     ssl = module.params['ssl']
-    ssl_cert_reqs = getattr(ssl_lib, module.params['ssl_cert_reqs'])
+    ssl_cert_reqs = None
+    if ssl:
+        ssl_cert_reqs = getattr(ssl_lib, module.params['ssl_cert_reqs'])
     roles = module.params['roles']
     state = module.params['state']
     update_password = module.params['update_password']