test: add systematic testing of all klog functions
test: add systematic testing of all klog functions

klog has a lot of functions, but not all of them are covered with unit
tests. Only a few check stack unwinding.

This new test is designed to:
- check stack unwinding for all functions
- check the difference between fmt.Print and fmt.Println (only the
  latter inserts spaces between strings)
- check the output with and without a Logger

This therefore covers bugs in https://github.com/kubernetes/klog/pull/280:
- depth was not passed on to Logger
- ErrorlnDepth and WarninglnDepth used fmt.Print instead of fmt.Println

kubernetes/klog,kubernetes/klog