kubetest: remove obsolete and redundant --logtostderr
kubetest: remove obsolete and redundant --logtostderr

It has been the default in klog for a long time and will be removed soon.

-vmodule continues to be supported. The way it is used here seems unnecessarily
complex, but perhaps there was a reason for it (like not conflicting with -v),
so that part is kept.

cjwagner/test-infra,dims/test-infra,kubernetes/test-infra,michelle192837/test-infra,BenTheElder/test-infra,BenTheElder/test-infra,michelle192837/test-infra,jessfraz/test-infra,cblecker/test-infra,kubernetes/test-infra,cblecker/test-infra,BenTheElder/test-infra,kubernetes/test-infra,cblecker/test-infra,michelle192837/test-infra,dims/test-infra,dims/test-infra,jessfraz/test-infra,michelle192837/test-infra,cjwagner/test-infra,cblecker/test-infra,cblecker/test-infra,BenTheElder/test-infra,cjwagner/test-infra,cjwagner/test-infra,jessfraz/test-infra,cjwagner/test-infra,michelle192837/test-infra,jessfraz/test-infra,BenTheElder/test-infra,jessfraz/test-infra,kubernetes/test-infra,dims/test-infra,BenTheElder/test-infra,dims/test-infra,jessfraz/test-infra,cblecker/test-infra,kubernetes/test-infra,michelle192837/test-infra,kubernetes/test-infra,dims/test-infra,cjwagner/test-infra