server: warn on migration of volumes within the same storage pool (#3424)

Added an if statement that catches the destination poolid as an invalid parameter if it is similer to the current poolid. 

Fixes #3291

Author: kioie

server/src/main/java/com/cloud/storage/VolumeApiServiceImpl.java

@@ -2033,6 +2033,10 @@ public Volume migrateVolume(MigrateVolumeCmd cmd) {
             throw new InvalidParameterValueException("Volume must be in ready state");
         }
 
+        if (vol.getPoolId() == storagePoolId) {
+            throw new InvalidParameterValueException("Volume " + vol + " is already on the destination storage pool");
+        }
+
         boolean liveMigrateVolume = false;
         Long instanceId = vol.getInstanceId();
         Long srcClusterId = null;
@@ -3384,4 +3388,4 @@ public String getConfigComponentName() {
     public ConfigKey<?>[] getConfigKeys() {
         return new ConfigKey<?>[] {ConcurrentMigrationsThresholdPerDatastore};
     }
-}
+}