Recipe which calculates free memory excludes buffers/cache

[cmilloy]

Hosts are being de-whitelisted because the memory considered to be "free" is under our threshold. This is problematic because there is plenty of memory in buffers and caches which could be offered by the mesos slave to run jobs.

We want to consider all memory in (free|buffer|cache) to be "free". I believe the change should go in the arguments for "sed" in satellite/satellite-slave/bin/satellite-recipes:

"free-memory") free -m | tr -s ' '| cut -d' ' -f4 | sed -n '3p'