Improve VM Monitoring with qemu-guest agent information

[dgarcia18]

Issue to keep track of the investigation on qemu-ga usage and its integration possibilities within the linux context packages.

VM crashing detection

The current monitoring system can not detect a VM crashing. This was tested with a kernel-panicked VM. With qemu-ga installed in the VM, a crash can be detected by the hypervisor. We can check if the VM has crashed with:
virsh qemu-agent-command one- '{"execute":"guest-ping"}'

The VM is not crashed if the exit code of the command is 0, meaning that the VM is replying to the qemu "ping".

[onenhansen]

We should try to also include:

• More in depth monitoring of the guest operating system, whatever is available from the QEMU Guest Agent (things like real memory usage inside the VM) - https://wiki.qemu.org/Documentation/QMP
• That information should also be available in the Prometheus probe if possible
• Dynamic Ballooning operations - Windows 10 guest not seeing free memory with balloon driver virtio-win/kvm-guest-drivers-windows#568

Examples:

# virsh qemu-agent-command --domain one-400 --cmd '{"execute": "guest-exec", "arguments": { "path": "wmic", "arg": ["OS", "GET", "TotalVisibleMemorySize"], "capture-output": true}}'
{"return":{"pid":1340}}

# virsh qemu-agent-command --domain one-400 --cmd '{"execute": "guest-exec", "arguments": { "path": "wmic", "arg": ["OS", "GET", "FreePhysicalMemory"], "capture-output": true}}'
{"return":{"pid":8372}}

# virsh qemu-agent-command --domain one-400 --cmd '{"execute": "guest-exec-status", "arguments": { "pid": 1340 }}' | jq -r '.return["out-data"]' | base64 -d
TotalVisibleMemorySize  
16757176                

# virsh qemu-agent-command --domain one-400 --cmd '{"execute": "guest-exec-status", "arguments": { "pid": 8372 }}' | jq -r '.return["out-data"]' | base64 -d
FreePhysicalMemory  
14303288   

# virsh qemu-monitor-command --hmp one-400 --cmd balloon 4096


# virsh qemu-agent-command --domain one-400 --cmd '{"execute": "guest-exec", "arguments": { "path": "wmic", "arg": ["OS", "GET", "FreePhysicalMemory"], "capture-output": true}}'
{"return":{"pid":8964}}

# virsh qemu-agent-command --domain one-400 --cmd '{"execute": "guest-exec-status", "arguments": { "pid": 8964 }}' | jq -r '.return["out-data"]' | base64 -d
FreePhysicalMemory  
1712584    

If possible, these values should also be extended to the Prometheus probe.