Update arm.sh to increase image size 3GB to 5GB
It seems some time around 25.7.10 the arm image does not
fit into 3 GB any more. The build would fail to create an
output image.
To give more room and also avoid future problems it is set to
5G.
build: add REMOTEDIR Makefile support again, fix nightly side effect
Also renames PRODUCT_SERVER to shorter SERVER because it's not really
part of the product. ;)
Allow the REMOTEDIR to be empty so we can automatically select a matching
directory in download/upload cases.