Changes the Kubelet configuration flag precedence order so that flags
take precedence over config from files/ConfigMaps.
See issue #56171 for more details.
Also modifies e2e node test suite to transform all relevant Kubelet
flags into a config file before starting tests when the
KubeletConfigFile feature gate is true, and turns on the
KubeletConfigFile gate for all e2e node tests. This allows the alpha
dynamic Kubelet config feature to continue to work in tests after
the precedence change.
Rather than just changing the config once to see if dynamic kubelet
config at-least-sort-of-works, this extends the test to check that the
Kubelet reports the expected Node condition and the expected configuration
values after several possible state transitions.
Additionally, this adds a stress test that changes the configuration 100
times. It is possible for resource leaks across Kubelet restarts to
eventually prevent the Kubelet from restarting. For example, this test
revealed that cAdvisor's leaking journalctl processes (see:
https://github.com/google/cadvisor/issues/1725) could break dynamic
kubelet config. This test will help reveal these problems earlier.
This commit also makes better use of const strings and fixes a few bugs
that the new testing turned up.
Related issue: #50217
