Small fixes for utils/{common_filters,common_params_for_list}

This is a follow-up of https://review.openstack.org/#/c/114555
addressing comments that were not addressed there.

* Add docstrings for both functions
* Make common_params_for_list check for correct limit
* Improve uint-tests coverage

Change-Id: I33bbb4eac4a91a935b42521b9c63e6ce2118cb31
Merge "Small fixes for utils/{common_filters,common_params_for_list}"