image.h: Include fcntl.h

No all distros (Rpi) provide O_PATH definition,
so include fcntl.h here thus we don't hit compilation
problem like

 |  CC       image.o
 | image.c: In function ‘open_image_at’:
 | image.c:187:29: error: ‘O_PATH’ undeclared (first use in this function)
Reported-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/image.h

@@ -6,6 +6,7 @@
 #include "compiler.h"
 #include "servicefd.h"
 #include "image-desc.h"
+#include "fcntl.h"
 #include "magic.h"
 
 #define PAGE_IMAGE_SIZE	4096