Gnulib already guarantees <stdbool.h>, so it is easier to just
use the standardized spellings.

* tools/virsh.c (vshCmdDef): Change callback to return real bool.
(__vshControl): Change several fields to bool.
(vshCommandOptBool): Change return type.
All callers updated.
* tools/Makefile.am (virsh-net-edit.c, virsh-pool-edit.c):
Likewise.