mounttest: wait for all background Close/Release after writing a file

The filesystem does a certain amount of things asynchronously waiting
for the file to be released after writing it means everything should
be in a consistent state.

cmd/mountlib/mounttest/write.go

@@ -2,7 +2,6 @@ package mounttest
 
 import (
 	"testing"
-	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -18,8 +17,7 @@ func TestWriteFileNoWrite(t *testing.T) {
 	err = fd.Close()
 	assert.NoError(t, err)
 
-	// FIXME - wait for the Release on the file
-	time.Sleep(10 * time.Millisecond)
+	run.waitForWriters()
 
 	run.checkDir(t, "testnowrite 0")
 
@@ -38,6 +36,8 @@ func FIXMETestWriteOpenFileInDirListing(t *testing.T) {
 	err = fd.Close()
 	assert.NoError(t, err)
 
+	run.waitForWriters()
+
 	run.rm(t, "testnowrite")
 }
 
@@ -68,6 +68,8 @@ func TestWriteFileOverwrite(t *testing.T) {
 //
 // NB the code for this is in file.go rather than write.go
 func TestWriteFileFsync(t *testing.T) {
+	run.skipIfNoFUSE(t)
+
 	filepath := run.path("to be synced")
 	fd, err := osCreate(filepath)
 	require.NoError(t, err)
@@ -77,4 +79,6 @@ func TestWriteFileFsync(t *testing.T) {
 	require.NoError(t, err)
 	err = fd.Close()
 	require.NoError(t, err)
+	run.waitForWriters()
+	run.rm(t, "to be synced")
 }