build:Only keep one ref to .settings and allow to override it.
Rreleasetools/arm_sdimage.sh uses a ".settings" file to allow to override
the defaults settings found in arm_sdimage. This change allows to use an
alternate file for this purpose. We figured out more programs (like eclipse)
use a ".settings" file.
One can tweak the settings files to use by settings the SETTINGS_MINIX
variable