NSFarm configuration and targets parsing

Currently targets are parsed in root conftest and there is no central NSFarm configuration. We need on top of targets configuration also some config with global settings. That is for shared resources. There is a potential that we can have some special fields for shared resources in target but we have to see.

• investigate need of additional config to allow definition of shared resources (such as Wi-Fi interfaces)
• Implement config parser and access and merge it with current target parser. That should be part of nsfarm not conftest.
• Add utility command for listing and analyzing provided configuration.

In other words we should take targets parsing from conftest and move it to for example nsfarm.config and extend it.