Fix FibreChannel volume plugin corrupting filesystem on detach

FibreChannel volume plugin misses one important step when removing a
device: "multipath -f". It flushes all multipath buffers to its individual
paths. Without it, a filesystem on the device may get corrupted.

pkg/volume/fc/fc_test.go

@@ -190,7 +190,7 @@ func doTestPlugin(t *testing.T, spec *volume.Spec) {
 
 	fakeManager2 := newFakeDiskManager()
 	defer fakeManager2.Cleanup()
-	unmounter, err := plug.(*fcPlugin).newUnmounterInternal("vol1", types.UID("poduid"), fakeManager2, fakeMounter)
+	unmounter, err := plug.(*fcPlugin).newUnmounterInternal("vol1", types.UID("poduid"), fakeManager2, fakeMounter, fakeExec)
 	if err != nil {
 		t.Errorf("Failed to make a new Unmounter: %v", err)
 	}