domblkstat: Produce error message that at least sounds like English

Compare:

  # virsh domblkstat freebsd hdd
  error: Failed to get block stats freebsd hdd
  error: invalid argument: invalid path: hdd

with:

  # virsh domblkstat freebsd hdd
  error: Failed to get block stats for domain 'freebsd' device 'hdd'
  error: invalid argument: invalid path: hdd
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

tools/virsh-domain-monitor.c

@@ -957,7 +957,7 @@ cmdDomblkstat(vshControl *ctl, const vshCmd *cmd)
         params = vshCalloc(ctl, nparams, sizeof(*params));
 
         if (virDomainBlockStatsFlags(dom, device, params, &nparams, 0) < 0) {
-            vshError(ctl, _("Failed to get block stats %s %s"), name, device);
+            vshError(ctl, _("Failed to get block stats for domain '%s' device '%s'"), name, device);
             goto cleanup;
         }