Empty table before adding primary key

The addition of the primary key can cause problems for populated tables
due to duplicate entries. Therefore we delete the existing data before
adding the primary key.

schema/mysql-migrations/upgrade_59.sql

@@ -1,3 +1,5 @@
+DELETE FROM vspheredb_daemonlog;
+
 ALTER TABLE vspheredb_daemonlog
   ADD PRIMARY KEY (instance_uuid, ts_create);