drive: fix DirMove leaving a hardlinked directory behind #2245

This bug was introduced by the v3 API conversion in 07f20dd1fd.

The problem was that dircache.FindPath doesn't work for the root directory.

This adds an internal error for dircache.FindPath being called with
the root directory.  This makes a failing test, which the fix to the
drive backend fixes.

This also improves the DirCache integration test.

fstest/fstests/fstests.go

@@ -626,6 +626,9 @@ func Run(t *testing.T, opt *Opt) {
 		fstest.CheckListing(t, remote, []fstest.Item{file1, file2})
 		// 1: file name.txt
 		// 2: hello sausage?/../z.txt
+
+		// Tidy up moveTest directory
+		require.NoError(t, remote.Rmdir("moveTest"))
 	})
 
 	// Move src to this remote using server side move operations.
@@ -664,21 +667,38 @@ func Run(t *testing.T, opt *Opt) {
 
 		// check remotes
 		// FIXME: Prints errors.
-		fstest.CheckListing(t, remote, []fstest.Item{})
+		// remote should not exist here
+		_, err = remote.List("")
+		require.Equal(t, fs.ErrorDirNotFound, errors.Cause(err))
+		//fstest.CheckListingWithPrecision(t, remote, []fstest.Item{}, []string{}, remote.Precision())
 		file1Copy := file1
 		file1Copy.Path = path.Join(newName, file1.Path)
 		file2Copy := file2
 		file2Copy.Path = path.Join(newName, file2.Path)
 		file2Copy.WinPath = path.Join(newName, file2.WinPath)
-		fstest.CheckListing(t, newRemote, []fstest.Item{file2Copy, file1Copy})
+		fstest.CheckListingWithPrecision(t, newRemote, []fstest.Item{file2Copy, file1Copy}, []string{
+			"new_name",
+			"new_name/sub_new_name",
+			"new_name/sub_new_name/hello? sausage",
+			"new_name/sub_new_name/hello? sausage/êé",
+			"new_name/sub_new_name/hello? sausage/êé/Hello, 世界",
+			"new_name/sub_new_name/hello? sausage/êé/Hello, 世界/ \" ' @ < > & ? + ≠",
+		}, newRemote.Precision())
 
 		// move it back
 		err = doDirMove(newRemote, newName, "")
 		require.NoError(t, err)
 
 		// check remotes
-		fstest.CheckListing(t, remote, []fstest.Item{file2, file1})
-		fstest.CheckListing(t, newRemote, []fstest.Item{})
+		fstest.CheckListingWithPrecision(t, remote, []fstest.Item{file2, file1}, []string{
+			"hello? sausage",
+			"hello? sausage/êé",
+			"hello? sausage/êé/Hello, 世界",
+			"hello? sausage/êé/Hello, 世界/ \" ' @ < > & ? + ≠",
+		}, remote.Precision())
+		fstest.CheckListingWithPrecision(t, newRemote, []fstest.Item{}, []string{
+			"new_name",
+		}, newRemote.Precision())
 	})
 
 	// TestFsRmdirFull tests removing a non empty directory