[test_fetchers] Removed unused urunparse import.
Removed an extra line-break.
In @gentests, get data from cls.data instead of from an argument
Move mock urlopen into test.support for future reuse.
Generalized mock urllib for using in all tests that need predictable HTTP responses.
Restored and fixed some discovery test that were never ran before.
Removed tests for discover.discover re-raising custom exceptions. No longer needed since it doesn't do any masking.
Use local variable for a mock, not urlopen in another module.
Restored URL normalization test in test_discover.