Proxmox ve plugin additions

[fdriessler]

General information

This PR adds 3 checks and changes 1 to extend monitoring of Proxmox guests that do not use a checkmk guest agent,
to allow monitoring of cpu, disk and network throughput as well as uptime, even if the guest doesnt use a Guest Agent.

Proposed changes

This PR is for the most part a extension of the proxmox_ve plugin, to improve monitoring of piggyback only guests.

Following changes were introduced:
Additional Check:

• proxmox_ve_cpu_util: Service that yields CPU Utilization stats for monitored VMs (as % and # of cores under load (this is just the % * max cpu cores available)). This service also allows for a optional Metric for a averaged Utilization Value.
• proxmox_ve_disk_throughput: Service that yields Disk Read/Write Throughput.
• proxmox_ve_network_throughput: Service that yields Net In/Out Throughput.
  Changed:
• proxmox_ve_vm_info: Addition of a Uptime

Additionally, 2 check_parameter files were renamed, so that all check_parameters for proxmox_ve follow a common naming scheme.