Detect machine GUID change

[stelfrag]

Summary

Currently, if you copy the entire /var/cache/netdata folder to a newly installed agent and then start the agent, the new system will use the existing history by switching the parent agent found in the metadata to the newly installed agent. In essence, the historical data from the old system is inherited by the new system.

With this change, the parent found in the copied data will be switched to an archived child node.

Test Plan

• Install a new agent (A) but don't start it
• Stop an existing agent (B) and copied it's /var/cache/netdata to agent (A)
• Start agent (A)
  • You should see data being collected for A
  • You should have an archived child with data from B

[thiagoftsm]

PR is working as expected, LGTM!