Introduce some basic infrastructure for doing domain ID allocation unit tests,
and add a few tests that ensure correctness of the domain ID allocator.
Use <xen-tools/bitops.h> and xen/lib/find-next-bit.c in test hardness code.
Adjust find-next-bit.c to be compiled with __XEN_TOOLS__.
Signed-off-by: Denis Mukhin <dmukhin@ford.com>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>