Add dry-run query param for HealFormat API (#3618)

pkg/madmin/API.md

@@ -251,13 +251,20 @@ __Example__
 ```
 
 <a name="HealFormat"></a>
-### HealFormat() error
+### HealFormat(isDryRun bool) error
 Heal storage format on available disks. This is used when disks were replaced or were found with missing format. This is supported only for erasure-coded backend.
 
 __Example__
 
 ``` go
-    err := madmClnt.HealFormat()
+    isDryRun := true
+    err := madmClnt.HealFormat(isDryRun)
+    if err != nil {
+        log.Fatalln(err)
+    }
+
+    isDryRun = false
+    err = madmClnt.HealFormat(isDryRun)
     if err != nil {
         log.Fatalln(err)
     }

pkg/madmin/examples/heal-format.go

@@ -39,8 +39,16 @@ func main() {
 		log.Fatalln(err)
 	}
 
-	// Heal storage format on available disks.
-	err = madmClnt.HealFormat()
+	// Attempt healing format in dry-run mode.
+	isDryRun := true
+	err = madmClnt.HealFormat(isDryRun)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	// Perform actual healing of format.
+	isDryRun = false
+	err = madmClnt.HealFormat(isDryRun)
 	if err != nil {
 		log.Fatalln(err)
 	}

pkg/madmin/heal-commands.go

@@ -344,7 +344,7 @@ func (adm *AdminClient) HealBucket(bucket string, dryrun bool) error {
 	queryVal.Set("heal", "")
 	queryVal.Set(string(healBucket), bucket)
 	if dryrun {
-		queryVal.Set(string(healDryRun), "yes")
+		queryVal.Set(string(healDryRun), "")
 	}
 
 	hdrs := make(http.Header)
@@ -378,7 +378,7 @@ func (adm *AdminClient) HealObject(bucket, object string, dryrun bool) error {
 	queryVal.Set(string(healBucket), bucket)
 	queryVal.Set(string(healObject), object)
 	if dryrun {
-		queryVal.Set(string(healDryRun), "yes")
+		queryVal.Set(string(healDryRun), "")
 	}
 
 	hdrs := make(http.Header)
@@ -405,9 +405,12 @@ func (adm *AdminClient) HealObject(bucket, object string, dryrun bool) error {
 }
 
 // HealFormat - heal storage format on available disks.
-func (adm *AdminClient) HealFormat() error {
+func (adm *AdminClient) HealFormat(dryrun bool) error {
 	queryVal := url.Values{}
 	queryVal.Set("heal", "")
+	if dryrun {
+		queryVal.Set(string(healDryRun), "")
+	}
 
 	// Set x-minio-operation to format.
 	hdrs := make(http.Header)