Add test summary

[ffaf1]

Make cabal-test tests will end with a useful summary:

⁝
ConfiguredPackage/License/UnknownLicence/cabal.test.hs                      OK (0.13s)
ConfiguredPackage/License/NoFileSpecified/cabal.test.hs                     OK (0.14s)
ConfiguredPackage/License/NoLicense/cabal.test.hs                           OK (0.13s)
OK
112 tests, 0 skipped, 0 unexpected passes, 0 unexpected fails.

This is useful when you are dealing with a lot of failures (e.g. refactoring) and an integer is more useful than a long list of test names.

---

Please include the following checklist in your PR:

• [x] Patches conform to the coding conventions.
• [x] Not a user change, nothing to write in a changeloc.
• [x] The documentation has been updated, if necessary.

Please also shortly describe how you tested your change. Bonus points for added tests!