test-http-bad-server: move on test from bytes-count to pattern
This specific test case is now using the new "close when a pattern is seen"
approach compared to the more fragile "that many bytes were sent" approach.
Since such change are still a bit noisy, we split each change in there own
changesets.
Differential Revision: https://phab.mercurial-scm.org/D12056
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL