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add ut for kuberuntime-gc
**What this PR does / why we need it**:
Add ut for kuberuntime-gc to cover more situations:
1) Add two uncovered cases to test sandbox-gc
(1) When there are more than one exited sandboxes,the older exited sandboxes without containers for existing pods should be garbage collected;
(2) Even though there are more than one exited sandboxes,the older exited sandboxes with containers for existing pods should not be garbage collected.
2) Add one uncovered case to test container-gc
(1) To cover the situation when allSourcesReady is set false;
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #
**Special notes for your reviewer**:
**Release note**:
```release-note
"NONE"
```
This also incorporates the version string into the package name so
that incompatibile versions will fail to connect.
Arbitrary choices:
- The proto3 package name is runtime.v1alpha2. The proto compiler
normally translates this to a go package of "runtime_v1alpha2", but
I renamed it to "v1alpha2" for consistency with existing packages.
- kubelet/apis/cri is used as "internalapi". I left it alone and put the
public "runtimeapi" in kubelet/apis/cri/runtime.
The enum constants are not namespaced. The shorter, unspecifc names are likely
to cause naming conflicts in the future.
Also replace "SandBox" with "Sandbox" in the API.
