Thrift autogenerated APIs needs a format fmt()

[gopakumarce]

thrift Exception type should have a "formatter" that prints the error string instead of deafult description(), like below
impl Display for InterfaceErr {
  fn fmt(&self, f: &mut Formatter) -> fmt::Result {
      if let Some(ref why) = (*self).why {
          write!(f, "{:?}", why)
      } else {
          self.description().fmt(f)
      }
  }
}