tests/helper-runtests.sh

test-http: add a (glob) for Windows

I'm not sure why the glob was ineffective with $TESTTMP here, but replacing it
with '*' works.

#
# Avoid interference from actual test env:

unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL