wic: Continue if excluded_path does not exist

If an excuded path does not exist, continue without an error.
This allows to seamleasly reuse .wks among different projects.

Eg:

part / --source rootfs --fstype=ext4 --exclude-path=opt/private_keys

Where /opt/private_keys in only populated by some of the image.bb files.

Cc: Paul Barker <pbarker@konsulko.com>
(From OE-Core rev: 2dbd692b8e563cf991fb4ae1ef6129fda0d7e3c4)

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

scripts/lib/wic/plugins/source/rootfs.py

@@ -136,7 +136,6 @@ class RootfsPlugin(SourcePlugin):
                     sys.exit(1)
 
                 full_path = os.path.realpath(os.path.join(new_rootfs, path))
-
                 # Disallow climbing outside of parent directory using '..',
                 # because doing so could be quite disastrous (we will delete the
                 # directory).
@@ -144,6 +143,9 @@ class RootfsPlugin(SourcePlugin):
                     logger.error("'%s' points to a path outside the rootfs" % orig_path)
                     sys.exit(1)
 
+                if not os.path.lexists(full_path):
+                    continue
+
                 if path.endswith(os.sep):
                     # Delete content only.
                     for entry in os.listdir(full_path):