capture klog output without SetBuffer

[pohly]

/kind feature

Describe the solution you'd like

There are several unit tests which temporarily use SetBuffer to capture log output. There have been several cases where this led to race conditions:

• kubelet: Race condition in nodeshutdown unit test kubernetes#108040
• Prevent race condition with bytes buffer in vsphere unit tests kubernetes#98944
• fix: race detected in TestErrConnKilled kubernetes#108553

Once we have contextual logging and the code under test supports it, SetBuffer can be removed and get replaced with a logger that writes into a byte.Buffer. Such tests then can run in parallel.

In klog we can provide such a logger. This has the advantage that the output format will be familiar.

Another alternative is a logger that captures the raw Info and Error parameters without formatting them. This may or may not be easier to test against.

[pohly]

/assign