Refactor API responsiveness tests which use klog

[tosi3k]

Current implementation of logging tests relies too much on turning off logging to stderr by klog which is possible to be done using a hack as below:

klog.InitFlags(nil)
flag.Set("logtostderr", "false")
flag.Parse()

Idea: introduce some Logger interface which will be easy to mock and will facilitate catching the log statements inside the unit tests.

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[wojtek-t]

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