expose properties as metric values if possible

[richardtief]

The vRops API exposes properties in various formats, so we represent them uniformly as metric labels. However, there are cases where the property value can be represented as a value (e.g. build numbers), which means that it is convertible to float.

• Check the different types of properties for vRops API.
• Implement a check in PropertiesCollector to represent them as values, if feasible.
• test and verify