wic: Add --embed-rootfs argument

This option adds the content of a rootfs on a specific location on the
rootfs.

It is very useful for making a partition that contains the rootfs for a
host and a target Eg:

/ -> Roofs for the host
/export/ -> Rootfs for the target (which will netboot)

Although today we support making a partition for "/export" this might
not be compatible with some upgrade systems, or we might be limited by
the number of partitions.

With this patch we can use something like:

part / --source rootfs --embed-rootfs target-image /export --embed-rootfs target-image2 /export2

on the .wks file.

(From OE-Core rev: efdcf94801f6abe8e4099e324d9a3deccd8d4384)

Signed-off-by: Ricardo Ribalda Delgado <ricardo@ribalda.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/wic/partition.py

@@ -31,6 +31,7 @@ class Partition():
         self.extra_space = args.extra_space
         self.exclude_path = args.exclude_path
         self.include_path = args.include_path
+        self.embed_rootfs = args.embed_rootfs
         self.fsopts = args.fsopts
         self.fstype = args.fstype
         self.label = args.label