cephfs: remove directory created in the ChangeDir test

The test function that exercises ChangeDir was creating a directory
and leaving it behind. Add some basic cleanup to the test to try
and avoid leaking stuff between test runs.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

cephfs/cephfs_test.go

@@ -130,6 +130,11 @@ func TestChangeDir(t *testing.T) {
 	assert.NotEqual(t, dir1, dir2)
 	assert.Equal(t, dir1, "/")
 	assert.Equal(t, dir2, "/asdf")
+
+	err = mount.ChangeDir("/")
+	assert.NoError(t, err)
+	err = mount.RemoveDir("/asdf")
+	assert.NoError(t, err)
 }
 
 func TestRemoveDir(t *testing.T) {