merge default metadata into drop-in kubelet config

[ndbaker1]

Issue #, if available:

Description of changes:

When using a KubeletConfiguration that lacks the metadata info like kind and apiVersion, this can cause kubelet's drop-in config merging to fail on a minimal config like:

{
  "maxPods": 2
}

E0202 20:46:59.510494   23792 run.go:74] "command failed" err=<
        failed to merge kubelet configs: failed to walk through kubelet dropin directory "drop-in-test/": failed to load kubelet dropin file, path: drop-in-test/test.conf, error: Object 'Kind' is missing in '{
            "maxPods": 2
        }
        '
 >

update the drop-in config path to merge user's data on top of default KubeletConfiguration metadata.

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Testing Done

update e2e tests to reflect the absence of kind and apiVersion

See this guide for recommended testing for PRs. Some tests may not apply. Completing tests and providing additional validation steps are not required, but it is recommended and may reduce review time and time to merge.

[Issacwww]

LGTM