Possible git permissions issue

[rsnape]

Noted on our totally clean install that I had to use sudo on the Pi Zero to run git pull. I think this is a bug, albeit a minor one. Probably because the make_mecs script installs git and clones etc with sudo privileges. Perhaps we should sudo -u pi for that one or similar.

[ggstuart]

Also mecs-update isn't used. It would be nice to fix it.

I think the problem was that the install step needed root privileges.

Should be possible to use sudo -u pi on the git pull, both in make_mecs and in mecs-update.