migration: introduce a delete_snapshot wrapper

Make snapshot deletion consistent with the snapshot save
and load commands by using a wrapper around the blockdev
layer. The main difference is that we get upfront validation
of the passed in device list (if any).

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20210204124834.774401-10-berrange@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
index 15d4e03..3c88a4f 100644
--- a/monitor/hmp-cmds.c
+++ b/monitor/hmp-cmds.c
@@ -1159,7 +1159,7 @@
     Error *err = NULL;
     const char *name = qdict_get_str(qdict, "name");
 
-    bdrv_all_delete_snapshot(name, false, NULL, &err);
+    delete_snapshot(name, false, NULL, &err);
     hmp_handle_error(mon, err);
 }