Add a xapi-to-sql command

[edwintorok]

This introduces a dependency on sqlite-utils.

When no output file is specified then the SQL is dumped to stdout.

For now nested maps are kept as JSON.
sqlite-utils could flatten,
but it requires all the flattened elements to have the same keys, which is not true for other-config and sm-config, etc.

Here is an example query:

SELECT VM.name_label, host.name_label, VM.domid from VM INNER JOIN VM_guest_metrics ON guest_metrics=VM_guest_metrics.ref INNER JOIN host ON resident_on=host.ref WHERE power_state='Running' AND PV_drivers_detected == "true" AND json_extract(PV_drivers_version, '$.micro')=='-1';

A similar query could be achieved with jq on the output of xapi-to-json, but it is cumbersome:

jq 'JOIN(INDEX(.host[]; .ref); JOIN(INDEX(.VM_guest_metrics[]; .ref); .VM[]; .guest_metrics; .); .[0].resident_on; .) | select(.[0][1].PV_drivers_detected == "true") | select(.[0][1].PV_drivers_version.micro? == "-1" // false) | select(.[0][0].power_state == "Running") | "\(.[0][0].name_label); \(.[1].name_label); \(.[0][0].domid)"'

[edwintorok]

If the added dependency is a concern it might be possible to figure out a way to make it optional, probably needs some fiddling with the python project file. Although keeping it as is would be simpler.