storage backend rbd: Do not prefix rbd: on volume names.

We used to prefix 'rbd:' to volume names, this is not necessary.

Qemu takes RBD devices in this way, like: qemu -drive rbd:pool/image

When attaching a network disk like RBD to a guest we however do not use this prefix.

Currently you can't map a RBD volume name directly to a domain without removing the prefix.
Signed-off-by: NWido den Hollander <wido@widodh.nl>

src/storage/storage_backend_rbd.c

@@ -237,7 +237,7 @@ static int volStorageBackendRBDRefreshVolInfo(virStorageVolDefPtr vol,
     vol->type = VIR_STORAGE_VOL_NETWORK;
 
     VIR_FREE(vol->target.path);
-    if (virAsprintf(&vol->target.path, "rbd:%s/%s",
+    if (virAsprintf(&vol->target.path, "%s/%s",
                     pool->def->source.name,
                     vol->name) == -1) {
         virReportOOMError();