qemu: Always set auth_supported for Ceph disks.

Recently the Ceph project defaulted auth_supported from 'none' to 'cephx'.

When no auth information was set for Ceph disks this would lead to librados defaulting to
'cephx', but there would be no additional authorization information.

We now explicitly set auth_supported to none when passing down arguments to Qemu.
Signed-off-by: NWido den Hollander <wido@widodh.nl>

src/qemu/qemu_command.c

@@ -1782,6 +1782,8 @@ qemuBuildRBDString(virConnectPtr conn,
                             disk->auth.username);
             goto error;
         }
+    } else {
+        virBufferAddLit(opt, ":auth_supported=none");
     }
 
     if (disk->nhosts > 0) {