storage: Introduce --inactive for pool-dumpxml

Storage is one of the last domains in libvirt where we don't fully
utilize inactive and live XML. Okay, it might be because we don't
have support for that. So implement such support. However, we need
to fallback when talking to old daemon which doesn't support this
new flag called VIR_STORAGE_XML_INACTIVE.

include/libvirt/libvirt.h.in

@@ -2445,6 +2445,10 @@ struct _virStorageVolInfo {
 
 typedef virStorageVolInfo *virStorageVolInfoPtr;
 
+typedef enum {
+    VIR_STORAGE_XML_INACTIVE    = (1 << 0), /* dump inactive pool/volume information */
+} virStorageXMLFlags;
+
 /*
  * Get connection from pool.
  */