add uri information on ConectionException

 Added Uri info on ConectionException, is very useful to debug network problems on environments with many Redis instances:

Predis\Connection\ConnectionException: Connection refused on tcp://127.0.0.1:6379/

 To pass all testSuite I was not able to find a way to assert ExpectedExceptionMessage, as connection attributes are not fixed, so i'd remove that annotation on ConnectionTestCase.