Some of the E2E node tests were flaky. Their timeout apparently was chosen
under the assumption that kubelet would retry immediately after a failed gRPC
call, with a factor of 2 as safety margin. But according to
0449cef8fd,
kubelet has a different, higher retry period of 90 seconds, which was exactly
the test timeout. The test timeout has to be higher than that.
As the tests don't use the gRPC call timeout anymore, it can be made
private. While at it, the name and documentation gets updated.
d11b58efe6