virsh: Provide completers for options taking comma separated list of disk targets

'--storage' of the 'undefine' command and '--migrate-disks' of the
'migrate' command take a list of disk targets as an argument.

We can simply combine 'virshDomainDiskTargetCompleter' with
'virshCommaStringListComplete' to provide the completions.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

tools/virsh-completer-domain.h

@@ -166,3 +166,13 @@ char **
 virshDomainStorageFileFormatCompleter(vshControl *ctl,
                                       const vshCmd *cmd,
                                       unsigned int flags);
+
+char **
+virshDomainMigrateDisksCompleter(vshControl *ctl,
+                                 const vshCmd *cmd,
+                                 unsigned int completeflags);
+
+char **
+virshDomainUndefineStorageDisksCompleter(vshControl *ctl,
+                                 const vshCmd *cmd,
+                                 unsigned int completeflags);