flash-image: Create a journal when the filesystem is being created

flash-image: Create a journal when the filesystem is being created

We recently started to have problems when a new installation was
launched from the flash image that creating the journal corrupted the
filesystem on the next mount operation.

Since we would like all IPFire installations to have a journal, we
create this now when we create the image and won't try to add it later.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>