Provide Buffer, cache memory along with free memory

[SumoSourabh]

Exact Use case as per Filip

I think it's also worth mentioning that when we look at "FreeMemory" that Jenkins reports, we can't really say that it's all available memory on the machine. To be precise, this measure means: FreeMemory = Total - Used - Buffer/Cache That means when Jenkins reports ~100M FreeMemory on a 8000M machine, it's possible that processes are using only ~400M, and remaining 7500M is used for cache. It would be great if you could report more memory information than free and total - what would be super useful is also reporting used