validators: don't catch all Exceptions as invalid clone URIs, be specific When adding a new repository with a remote clone URI, the URI will be validated in some way. Several exceptions could occur during that validation. Previously, the code would catch based on 'Exception', which means that _any_ exception would cause the URI to be found invalid. This means that errors in the code (e.g. related to Python 3 conversion) were also categorized as 'invalid clone URI'. And thus, the tests that test an actually invalid URI would pass, even though there was a bug. Now, things have been refactored so it only is relevant to catch InvalidCloneUriException. Any other exception will now yield a 500 Internal Server Error, as expected.