virsh: Set up cmdDomblkinfo() and cmdDomblkinfoPrint() for vshTable API implementation

virsh: Set up cmdDomblkinfo() and cmdDomblkinfoPrint() for vshTable API implementation

I've moved all the printing from cmdDomblkinfoPrint() to cmdDomblkinfo(),
and renamed the cmdDomblkinfoPrint() to cmdDomblkinfoGet(), since nature of
that function changed from gathering and printing informations only to
gathering information. This I believe simplifies the functions and
makes the implementation of vshTable API simpler.

Signed-off-by: Simon Kobyda <skobyda@redhat.com>