img: Introduce the notion of a raw image

Raw images are supposed to be files with non-crtools contents.
E.g. tarballs with tmpfs contents or iptables-save output. Another
example is -- ip tool addr and route dumps we're about to merge
soon.

Having these type of images allows to use the open_image and the
cr_fdset engine easily.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/image.h

@@ -10,6 +10,13 @@
 
 #define CRTOOLS_IMAGES_V1	1
 
+/*
+ * Raw images are images in which data is stored in some
+ * non-crtool format (ip tool dumps, tarballs, etc.)
+ */
+
+#define RAW_IMAGE_MAGIC		0x0
+
 /*
  * The magic-s below correspond to coordinates
  * of various Russian towns in the NNNNEEEE form.