Getting rid of the "Mounted!" message makes it easier
to integrate into xfstests, which barks at all and any
unexpected output.

Used by https://github.com/rfjakob/fuse-xfstests/commit/ab1d77ccdb8cf16f79cb312bcb3aaadb23660807

Change-Id: Idff314474b4980ef6f6fc2460b338a840bb0e409