Change in ovirt-guest-agent[master]: agent: Implement basics for API Versioning

[vfeenstr at redhat.com]

Vinzenz Feenstra has submitted this change and it was merged.

Change subject: agent: Implement basics for API Versioning
......................................................................


agent: Implement basics for API Versioning

This commit introduces the basics needed to support API versioning between
the ovirt-guest-agent and VDSM.

How the negotiation works:
- VDSM has as a default the apiVersion value set to _DISABLED_API_VALUE marking
  it as unsupported
- The guest agent sends its max supported version with every `heartbeat`
  message
- VDSM checks that `apiVersion` exists in the `heartbeat` message arguments
  - If it exists it retrieves the minimum common version and sends the
    `api-version` message with the common version as `apiVersion` argument
  - If it does NOT exist it and the apiVersion is not set to
    _DISABLED_API_VALUE it will set it to _DISABLED_API_VALUE, with the meaning
    that it is not supported at all by the guest agent on the other end.
- The guest agent on receiving this message makes it own check and sets the
  `apiVersion` to the commonVersion

- If VDSM sends the `refresh` command it also sends its `apiVersion` value
  however if it does not, capable guest agents are disabling the versioning
  support and will know it in pre-supported state as well.

NOTE: VDSM will never send an api-version message without being triggered.
      This is to ensure backwards compatibility.

Change-Id: I754d52009538914dd0143894b24ad48fbf13cb38
Signed-off-by: Vinzenz Feenstra <vfeenstr at redhat.com>
---
M ovirt-guest-agent/OVirtAgentLogic.py
M tests/guest_agent_test.py
M tests/message_validator.py
3 files changed, 170 insertions(+), 24 deletions(-)

Approvals:
  Vinzenz Feenstra: Verified; Looks good to me, approved
  Francesco Romani: Looks good to me, but someone else must approve



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Gerrit-MessageType: merged
Gerrit-Change-Id: I754d52009538914dd0143894b24ad48fbf13cb38
Gerrit-PatchSet: 12
Gerrit-Project: ovirt-guest-agent
Gerrit-Branch: master
Gerrit-Owner: Vinzenz Feenstra <vfeenstr at redhat.com>
Gerrit-Reviewer: Francesco Romani <fromani at redhat.com>
Gerrit-Reviewer: Martin Sivák <msivak at redhat.com>
Gerrit-Reviewer: Michal Skrivanek <michal.skrivanek at redhat.com>
Gerrit-Reviewer: Roy Golan <rgolan at redhat.com>
Gerrit-Reviewer: Vinzenz Feenstra <vfeenstr at redhat.com>
Gerrit-Reviewer: automation at ovirt.org
Gerrit-Reviewer: oVirt Jenkins CI Server