Kata Containers shim support

[sameo]

The Kata Containers shim needs the following parameters:

• The agent URL (Or the proxy one when there is a proxy)
• The container ID
• The guest process token it monitors

As a consequence, the virtcontainers support for the Kata Containers shim needs:

• [X] Addition of a new shim type for Kata Containers
• [X] Implementation of the Kata Container shim (i.e. its start() method)

[sameo]

@jodh-intel Good points. I added some comments, let me know if that's clearer now.

[sboeuf]

@sameo according to https://github.com/kata-containers/agent/pull/83, I think you can remove your first commit agent: Return guest process information when starting a new one. We need another PR for virtcontainers in order to generate some unique IDs for every processes.

[sameo]

@sboeuf @jodh-intel This is ready to review.

[jodh-intel]

CI is unhappy:

13:57:32 Run go test and generate coverage:
14:02:32 Build timed out (after 5 minutes). Marking the build as aborted.
14:02:32 Build was aborted

[sameo]

@jodh-intel

CI is unhappy

This should be fixed now.

[sboeuf]

LGTM