Bind-mount vfs directories for each stage

Many of the stages need it anyway.

osbuild

@@ -58,6 +58,10 @@ def main(pipeline_path, from_archive, save):
                 set -e
                 mount -t tmpfs tmpfs /tmp
                 mount -t tmpfs tmpfs /var/tmp
+                mkdir -p {tree}/dev {tree}/sys {tree}/proc
+                mount --bind /dev {tree}/dev
+                mount --bind /sys {tree}/sys
+                mount --bind /proc {tree}/proc
                 stages/{name}
             """