Many images have 'if x86_64 then amd64 elif aarch64 then arm64' check to
comply with Debian like architecture names in several projects.
This patch creates 'debian_arch' variable which can be used in all
Docker files (similar to 'base_arch' one).
All required images got converted to use it.
Change-Id: I9c5e6f13d6c9b24fe323408512bd5aef290111ad