xl: enable using ranges of pCPUs when creating cpupools

xl: enable using ranges of pCPUs when creating cpupools

instead of just list of single pCPUs or NUMA node IDs, as
it happens right now.

On the other hand, after this change, strings containing
pCPUs and NUMA node ranges is supported. The syntax is the
same one supported by the "cpus" and "cpus_soft" config
switch, i.e., "4-8" or "node:1,12-18,^14".

This make things more flexible, more consistent, and also
improves error handling, as the pCPU range parsing routine
already present in xl is more reliable than just a call
to atoi().

While there, remove a redundant error check in the legacy syntax
handling (libxl_bitmap_test() already checks the index being
within the size of the bitmap).

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Cc: Juergen Gross <JGross@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>