Remove trailing '='s from unittests for networkstatus.parseRLine().

Because of the bug fixed in the last commit, two unittests in
`test_parse_networkstatus.ParseNetworkStatusRLineTests` now FAIL. They
are:

  ø test_invalidDescriptorDigest_missingBase64padding
  ø test_invalidIPAddress
Update unittest parameter docstrings for parseRLine() tests.
Fix lengths of base64 fields in unittests for parseRLine().

In real `@type bridge-networkstatus` documents, the base64 fields are 27
characters in length, not 29 characters.