The functions

	- dir_clonepaths();
	- dir_create();
	- dir_destroy();
	- dir_detect();
	- dir_mount();
	- dir_umount();

move from bdev.c to lxcdir.{c,h}. All functions which previously were static
become extern.

Adapt Makefile.am to include lxcdir.{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 lxcdir.h as the functions
associated with dir need access to it.
Signed-off-by: Christian Brauner <christian.brauner@mailbox.org>