py3: re-implement the BaseHTTPServer.test() function
The function is changed in python 3. So the latest version of function is
re-implemented. One can look at https://hg.python.org/cpython/file/3.5/Lib/http/server.py#l1184
and https://hg.python.org/cpython/file/2.7/Lib/BaseHTTPServer.py#l590 to see the change
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL