Switch from glog to klog

[jdolitsky]

Please see the following explanation of the reasons for klog vs. glog: https://github.com/kubernetes/klog#why-was-klog-created

[jdolitsky]

This should pull in latest go-licenses once this is merged: https://github.com/google/go-licenses/pull/138

[mhutchinson]

/gcbrun

I've just rebased this to fix conflicts in the go.mod file

[mhutchinson]

This is currently failing presubmit checks because klog.Fatalf is not recognized as an exit condition, and we're getting staticcheck errors from this. This is fixed (https://github.com/dominikh/go-tools/pull/1110) but we'll need to update the libraries. Error:

running golangci-lint
experimental/batchmap/cmd/verify/verify.go:101:6: SA5011(related information): this check suggests that the pointer can be nil (staticcheck)
		if leaf == nil {
		   ^

[mhutchinson]

I've got #2791 to update to the latest linter, but it doesn't fix this problem. https://github.com/dominikh/go-tools/blob/v0.3.3/go/ir/exits.go#L100 - looks like more work is required upstream in the staticcheck library to detect the v2 version of klog.

[AlCutter]

/gcbrun

[AlCutter]

I've rebased/jimmied onto HEAD and fixed a few follow-up bits, @hickford would you mind casting an eye over the tweaks so I'm not approving my own code?

[AlCutter]

Added #2801 to track removing the //nolint comments once @mhutchinson's fix to golangci-lint is present in a released version.