Add twisted errors to list of Fido timeouts

[bplotnick]

This fixes #344 by adding twisted.internet.error.DNSLookupError and twisted.internet.error.ConnectingCancelledError to the list of timeout errors.

As mentioned in the issues, these seem like more general than just timeouts, but I can reliably reproduce them by setting low request timeouts, so they should probably be caught somehow.

[macisamuele]

@bplotnick sorry for the late reply
I'm personally a bit against this change because the errors that you're adding to timeout_errors are more like connection errors.
I planned to add the same handling for connection errors (defining BravadoConnectionErrors) but I was not able to have reliable integration tests.

[bplotnick]

@macisamuele Yeah I am not too happy with this either because the errors could probably be caused by other issues. However, I'm not entirely sure what the alternative is. Could we put some sort of "reasonable" minimum timeout? Is that going to be reliable?