bpo-37411: Rewrite test_wsgiref.testEnviron() (GH-14394)

Fix test_wsgiref.testEnviron() to no longer depend on the environment
variables (don't fail if "X" variable is set).

testEnviron() now overrides os.environ to get a deterministic
environment. Test full TestHandler.environ content: not only a few
selected variables.
2 files changed