Proposal: refactor runtime-tools commands

[hqhq]

We use oci-runtime-tool validate to validate bundle and use make localvalidation for runtime validation, it doesn't look ideal to me, what I thought is:

• oci-runtime-tool generate for config generation
• oci-runtime-tool validate bundle for bundle validation
• oci-runtime-tool validate runtime for runtime validation

As the only tool we offer to user is oci-runtime-tool and runtimetest is only an auxiliary binary for runtime validation, I think runtimetest should not be taken as a first class citizen as oci-runtime-tool is. So I think we should move oci-runtime-tool main code to root directory and put runtimetest codes into some sub directories, put them in cmd directory and generate the two binaries in root directory looks like we are offering two tool binaries.

WDYT about this refactoring, I can help working on this if it looks good to you.

[hqhq]

ping @Mashimiao @liangchenye @mrunalp

[liangchenye]

localvalidation is a temporary solution, runtimetest only partially validate a runtime with the spec.
What we miss is a runtime testing framework which was discussed before and was assigned to me....
It should start/stop/kill a runtime and verify the running status.

I think we can refactor it according to your suggestion after the testing framework been implemented.

[Mashimiao]

runtimetest is a necessary binary to check container's internal environment. At first we also want something like oci-runtime-tool validate runtime. But as reasons which have been discussed in #336, we decided to use make localvalidation

[Mashimiao]

But I really prefer to something like oci-runtime-tool validate runtime, if we can solve problems in #336