bug fix: log over-written in twoStageRsyncProvider

solve more DATA RACE problem

worker/provider_test.go

@@ -79,11 +79,12 @@ exit 0
 			err = ioutil.WriteFile(scriptFile, []byte(scriptContent), 0755)
 			So(err, ShouldBeNil)
 
+			targetDir, _ := filepath.EvalSymlinks(provider.WorkingDir())
 			expectedOutput := fmt.Sprintf(
 				"syncing to %s\n"+
 					"%s\n"+
 					"Done\n",
-				provider.WorkingDir(),
+				targetDir,
 				fmt.Sprintf(
 					"-aHvh --no-o --no-g --stats --exclude .~tmp~/ "+
 						"--delete --delete-after --delay-updates --safe-links "+
@@ -144,11 +145,12 @@ exit 0
 			err = ioutil.WriteFile(scriptFile, []byte(scriptContent), 0755)
 			So(err, ShouldBeNil)
 
+			targetDir, _ := filepath.EvalSymlinks(provider.WorkingDir())
 			expectedOutput := fmt.Sprintf(
 				"syncing to %s\n"+
 					"%s\n"+
 					"Done\n",
-				provider.WorkingDir(),
+				targetDir,
 				fmt.Sprintf(
 					"%s %s -aHvh --no-o --no-g --stats --exclude .~tmp~/ "+
 						"--delete --delete-after --delay-updates --safe-links "+
@@ -306,6 +308,7 @@ exit 0
 			err = provider.Run()
 			So(err, ShouldBeNil)
 
+			targetDir, _ := filepath.EvalSymlinks(provider.WorkingDir())
 			expectedOutput := fmt.Sprintf(
 				"syncing to %s\n"+
 					"%s\n"+
@@ -313,14 +316,14 @@ exit 0
 					"syncing to %s\n"+
 					"%s\n"+
 					"Done\n",
-				provider.WorkingDir(),
+				targetDir,
 				fmt.Sprintf(
 					"-aHvh --no-o --no-g --stats --exclude .~tmp~/ --safe-links "+
 						"--timeout=120 --contimeout=120 --exclude dists/ -6 "+
 						"--exclude-from %s %s %s",
 					provider.excludeFile, provider.upstreamURL, provider.WorkingDir(),
 				),
-				provider.WorkingDir(),
+				targetDir,
 				fmt.Sprintf(
 					"-aHvh --no-o --no-g --stats --exclude .~tmp~/ "+
 						"--delete --delete-after --delay-updates --safe-links "+