Allow selecting another rootfs

I built a pine64 A64 device rootfs to reduce the time and effort
we spend inside debos. This allows selecting that instead of the default

mainline-rootfs-core.yaml

 {{- $architecture := or .architecture "arm64" -}}
 {{- $debug := or .debug "off" -}}
+{{- $imagesuffix := or .imagesuffix "-edge" -}}
 
 architecture: {{ $architecture }}
 actions:
   - action: download
     description: Download latest ubuntu touch rootfs from CI
-    url: "https://ci.ubports.com/job/xenial-mainline-edge-rootfs-{{ $architecture }}/lastSuccessfulBuild/artifact/out/ubuntu-touch-xenial-edge-{{ $architecture }}-rootfs.tar.gz"
+    url: "https://ci.ubports.com/job/xenial-mainline{{ $imagesuffix }}-rootfs-{{ $architecture }}/lastSuccessfulBuild/artifact/out/ubuntu-touch-xenial{{ $imagesuffix }}-{{ $architecture }}-rootfs.tar.gz"
     unpack: false
     filename: ut-rootfs.tar.gz
     name: ut-rootfs.tar.gz

pine64-common.yaml

@@ -10,6 +10,7 @@ actions:
     variables:
       architecture: {{ $architecture }}
       debug: {{ $debug }}
+      imagesuffix: "-edge-pine"
 
   - action: run
     chroot: true