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.
Merge commit 'e4bf2c211a81a3aee52241e4f73d929e2c3759ba' into HEAD