Automatic merge from submit-queue (batch tested with PRs 48890, 46893, 48872, 48896)
Support customized system spec in the node conformance test and create the GKE system spec
ref: https://github.com/kubernetes/kubernetes/issues/46891
- System specs are located in `test/e2e_node/system/specs`. Created one for validating GKE images in `test/e2e_node/system/specs/gke.yaml`.
- `--image-spec-name` can be used to specify a system spec in node e2e and conformance tests. This option maps to `SYSTEM_SPEC_NAME` in a test properties file, which is the user facing configuration. So, users can specify `SYSTEM_SPEC_NAME=gke` to run the image validation using the GKE system spec.
- If `SYSTEM_SPEC_NAME` is unspecified, the default spec (`system.DefaultSysSpec`) will be used.
- We can also use `make test-e2e-node SYSTEM_SPEC_NAME=gke` to run tests using GKE image spec.
**Release note**:
`None`
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