deactivate qgis_wcsprovidertest

Disabling on behalf of @m-kuhn since the wcs server used in qgis_wcsprovidertest is not really reliable. Often the test fails due to server problem.
We should use a more solid server or make the test handle connections problems
Merge pull request #1697 from mbernasocchi/patch-1

deactivate qgis_wcsprovidertest on travis

It depends on an unreliable external service and therefore produces false alarms.