These tests upload contents and randomly make the server start to
respond before the client finishes to upload data, making the test
occasionally fail. Waiting for a body in the server doesn't always
work, depending on the method or how the data are advertised. Thus,
let's ask haproxy to wait for the request using the aforementioned
option, it guarantees that the DATA frame is sent before the response
HEADERS frame is delivered.
These tests send GET/HEAD/POST requests in H1 and H2, with and without
HTX, with and without a body, and verify that the behaviour is the expected
one. For now HEAD requests have been commented out because in H1 they are
not really testable as varnishtest expects to read a body, and in H2 the
behaviour depends on HTX/legacy, indicating a bug in haproxy (it looks
like we can deliver some data in response to HEAD in legacy mode).
