bpo-29887: Test normalization now fails if download fails (#905)

* test_normalization fails if download fails

bpo-29887. The test is still skipped if "-u urlfetch" option is not
passed to regrtest (python3 -m test -u urlfetch test_normalization).

* Fix ResourceWarning in test_normalization

bpo-29887: Fix ResourceWarning in test_normalization if tests are
interrupted by CTRL+c.