test-http-bad-server: introduce socket closing after reading a pattern
We introduce the `close-after-recv-patterns` option. It has the same goal as
`close-after-send-patterns` with a slightly different implementation.
Reading "up to a pattern" is hard. As we can only check the pattern from what we
have already read (inlike writing, were we can check what we are about to
write).
So instead we make the `close-after-recv-patterns` alter the behavior of the
existing `close-after-recv-bytes`. The value from `close-after-recv-bytes` only
gets into play after we have seen the pattern from `close-after-recv-patterns`.
This allow us to achieve the target benefit without changing the read pattern
too much.
Differential Revision: https://phab.mercurial-scm.org/D12068