fix(HttpClient): turn res stream to readable in HttpClient

[hekike]

Turn res stream readable immediately to make it possible to consume later in inherited clients.

[coveralls]

Coverage remained the same at 87.024% when pulling 3231c45 on fix/node-10-res-readable into 1edd6da on master.

[misterdjules]

Can you elaborate on why this is needed?

[misterdjules]

Great catch @hekike!

To give a bit more details: it seems the regression was introduced by nodejs/node@cf5f986, which effectively makes adding a 'readable' listener stay in non-flowing mode even after a 'data' event listener is added to the same stream.

That change was released with Node.js v10.0.0. Before that change, adding a 'data' event listener to a stream would always make it "flow". It's a bit unfortunate that it doesn't seem to be listed anywhere in the list of backward incompatible changes.

Long term, ideally we would not mix both streaming modes if possible, and we would use read() instead of .on('data'. but that would potentially be a bit involved, and so for the near term your fix looks good to me.

[misterdjules]

nit: It could be useful to add a bit more info about why that is necessary (maybe add the link to the PR in the nodejs repo?).

[misterdjules]

It's a bit unfortunate that it doesn't seem to be listed anywhere in the list of backward incompatible changes.

My apologies, it is listed, since all major changes are listed in the changelog (look for SEMVER-MAJOR and readable).