Correctly propagate errors sent with trailer headers

[dryajov]

The changes in ipfs/js-ipfs#1036 have introduced errors through Trailer headers (x-stream-error), however, due to the way trailer headers are and our use of streams we can't correctly propagate them.

This is mainly a chicken and egg problem:

1. we can't get Trailer headers unless the response ends
2. we can't propagate the error, because the response stream ended

Since the processing of the request happens with through stream, once the response ends, our through streams end too, before getting a chance to communicate the error to them. We will possibly need to do some reworking of how we process responses because of that.

[dryajov]

issues has been handled in - #636