Use tmpfs in order to build arm/v7 and linux/386 images again

[jonasalfredsson]

Use tmpfs in order to build arm/v7 and linux/386 images again

[JonasAlfredsson]

It looks like both the Debian and Alpine builds take around 60 minutes to complete (it is the arm/v7 arch that takes this long), so I have set timeouts of 100 minutes on both of them. If it takes longer than that we can be quite confident in that something is stuck and will probably need a restart.

[JonasAlfredsson]

After building the images i included a df -h printout, and it looks like this for the Debian and Alpine builds:

Debian

 Filesystem      Size  Used Avail Use% Mounted on
tmpfs           4.0G  1.9G  2.2G  47% /var/lib/docker
overlay         4.0G  1.9G  2.2G  47% /var/lib/docker/overlay2/7b36675853fbad6949dbfc1b458024102528d22c00d77e57186d636dabb55697/merged

Alpine

 Filesystem      Size  Used Avail Use% Mounted on
tmpfs           4.0G  1.2G  2.9G  28% /var/lib/docker
overlay         4.0G  1.2G  2.9G  28% /var/lib/docker/overlay2/05871bb04a4be62acbcd50da4dc6502509be4ca5875a1f432853f6f8c27d2a4d/merged

So I suppose it is about 2G for Debian and 1.3G for Alpine, however, if I lower the size of the tmpfs volume below 4G I ran into some "no space left on device" errors, so I guess more is needed during the unpacking and building phase.