RAMBar - show available memory in the old way

Old way means handle cached memory like it was free, subtract it from total.
Also use the internal MemoryInfo class instad of reading from /proc/meminfo.

Change-Id: I96462ed5f1b6923ec8fc4405b225d57691dd1aa0
Signed-off-by: Gergely Szell (sethyx) <szell@hu.ibm.com>