snapd should be excluded from OOM

[Oliver Grawert]

if you check a running ubuntu-core all-snap image for the diferent OOM core adjustments you can notice that only udevd and sshd are currently excluded from the OOM handling (values of -1000 on /proc/$pid/oom_score_adj mean a process will not be touched by the OOM scheduler) i.e. see:

http://paste.ubuntu.com/23274608/

which runs a script that finds all processes where oom_score_adj is not 0 ...
snapd should be among these processes to make sure a memory hungry snap package can not kill the managing daemon by occupying all ram.

adding a value of -1000 to /proc/$(pidof snapd)/oom_score_adj should become a default to guarantee an always available snapd process.