make REST client actually return headers when http method is HEAD

[migueldiascosta]

ported from hpcugent/vsc-base#276

(not sure where to put the test now)

[boegel]

@migueldiascosta W.r.t. your question on the test: the tests for the modules ingested from vsc-base were not copied into the framework repository.

I think that's OK for now, since we will have tests for the EasyBuild functionality that relies on the easybuild.base.* modules anyway.

Another option is to start a new test/framework/base.py test suite to cover changes/fixes made in easybuild.base.*.

In this case however, the change made here well eventually be covered (indirectly) via #2553, so I think it's fine.

[migueldiascosta]

@boegel yeah, those were precisely the options I was wondering about, and I agree that either way it should be fine

[boegel]

Thanks for the backport @migueldiascosta!