MemoryMonitor: use /proc/*/oom_score_adj rather than /proc/*/oom_adj

This change is based on a change made originally to luna-sysmgr by Simon
Busch, at

https://github.com/openwebos/luna-sysmgr/commit/fdf37758e36da98268da95051cb6

On newer kernels /proc/*/oom_adj is deprecated and should not be used anymor
webOS requires at least a linux 3.3 kernel this changes the use to the new
/proc/*/oom_score_adj entry but still keeps backward compatiblity for older
kernels that provide /proc/*/oom_adj.

More information about the change are available on the following pages:
- https://github.com/mirrors/linux-2.6/commit/a63d83f427fbce97a6cea0db2e64b0
- https://www.redhat.com/archives/lvm-devel/2011-July/msg00097.html

Open webOS DCO 1.0 Signed off by Simon Busch [morphis@gravedo.de]
Open-webOS-DCO-1.0-Signed-off-by: Eric Blade <eric.blade@palm.com>

Change-Id: I8fd3d4acd2ce71338391bad0e231fce1869160e6