The functions

	- rbd_clonepaths();
	- rbd_create();
	- rbd_destroy();
	- rbd_detect();
	- rbd_mount();
	- rbd_umount();

move from bdev.c to lxcrbd.{c,h}. All functions previously declared static
become extern.

Adapt Makefile.am to include lxcrbd.{c,h}.

The structs

       - struct bdev; /* defined in bdev.h */
       - struct bdev_specs; /* defined in lxccontainer.h */
       - struct lxc_conf; /* defined conf.h */

are forward declared/put as incomplete types into lxcrbd.h as the functions
associated with rbd need access to it.

Put:

       - #define __STDC_FORMAT_MACROS

and include:

       - #include <inttypes.h>

in lxcrbd.c so that the format specifier PRIu64 is available.
Signed-off-by: Christian Brauner <christian.brauner@mailbox.org>