Improve parameterized test with parameter value in name
Test mergeBase in two additional paths
Randomize credentials test order, and limit to 3 tests

Rely on a multi-configuration job on several platforms to cover
all the authentication configurations at least once.  Reduces test
time without too serious a compromise in test coverage.

Allows me to define many authentication test cases without
significantly worse test execution performance.
Remove credentials test task from README - credentials test is written
Use variable in test name, improve diagnostic clarity