Fixing functional tests on #next

CHANGELOG:

- removed the error handler from `lib/middleware.js` and instead allow application to setup their own error handler. if not specified, the default `express` one will be used.
- updated `lib/middleware/mojito-tunnel-*` for functional tests to pass
- updated `tests/run.js` to ignore set of tests to be revisited or removed later; could not find a way to disable those tests in arrow descriptor configuration.


TESTS TO REVISIT (or disabled permanently ?)

The following tests have been disabled (no html5app and context appConfig in #next yet).

```
'html5apptest_descriptor.json',                                         
'configtest0_descriptor.json',                                          
'configtest1_descriptor.json',                                          
'configtest2_descriptor.json',                                          
'configtest3_descriptor.json',                                          
'configtest4_descriptor.json',                                          
'configtest5_descriptor.json',                                          
'configtest6_descriptor.json',                                          
'simple_logging_descriptor.json'  
```