Change formula for calculating free memory

[chetjain]

Current method uses free field in the 'free -m' command to calculate unused memory.
[root@ktebackup ~]# free -h
total used free shared buff/cache available
Mem: 177Gi 48Gi 19Gi 2.3Gi 110Gi 101Gi
Swap: 4.0Gi 80Mi 3.9Gi

Before doing so, it also try to flush the memory(sync) in buff/cache to add it to 'free' field.

RunCommand("sync", tlog, 2, 0)
706 RunCommand("echo 3 > /proc/sys/vm/drop_caches", tlog, 2, 0)

However this method cause the sync command to get hung sometime, when the nfs i/o is heavy or due to other busy I/O activity.
Few bugs are opened against RH. nothing resolved. So we want to escape above two steps, as this will unnecessarily stop SLS execution

[chetjain]

Created pull request #50