Fix missing metadata trailer in StatusErrors

[emeroad]

StatusErrors is not processing metadata trailer

https://github.com/grpc/grpc-java/blob/master/examples/src/main/java/io/grpc/examples/errorhandling/DetailErrorSample.java

static void verifyErrorReply(Throwable t) {
    Status status = Status.fromThrowable(t);
    Metadata trailers = Status.trailersFromThrowable(t);
    Verify.verify(status.getCode() == Status.Code.INTERNAL);
    Verify.verify(trailers.containsKey(DEBUG_INFO_TRAILER_KEY));
    Verify.verify(status.getDescription().equals(DEBUG_DESC));
    try {
      Verify.verify(trailers.get(DEBUG_INFO_TRAILER_KEY).equals(DEBUG_INFO));
    } catch (IllegalArgumentException e) {
      throw new VerifyException(e);
    }
  }