Add further tests for WMS

Example test config:

    | Check ads layer exists  |
    |                         | Set service url             | ${WMS_URL}           |
    |                         | ${layer_exists}             | Check for wms layer      | ospremium               |
    |                         | Should Be True              | ${layer_exists}          |

    | Check ads layers getmap |
    |                         | Set service url             | ${WMS_URL}           |
    |                         | Check advertised wms layers |

Also a few PEP8 fixes in the second commit ;-)