Fixes multiple device deleting issue

Fixes entgra/product-iots#656

components/device-mgt/org.wso2.carbon.device.mgt.core/src/main/java/org/wso2/carbon/device/mgt/core/service/DeviceManagementProviderServiceImpl.java

@@ -150,6 +150,7 @@ import java.io.IOException;
 import java.io.StringWriter;
 import java.sql.SQLException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Calendar;
 import java.util.Collections;
 import java.util.Date;
@@ -613,7 +614,6 @@ public class DeviceManagementProviderServiceImpl implements DeviceManagementProv
             DeviceManagementDAOFactory.closeConnection();
         }
 
-        try {
         DeviceCacheKey deviceCacheKey;
         for (Device device : existingDevices) {
             if (!EnrolmentInfo.Status.REMOVED.equals(device.getEnrolmentInfo().getStatus())) {
@@ -633,11 +633,12 @@ public class DeviceManagementProviderServiceImpl implements DeviceManagementProv
             if (deviceIdentifierMap.containsKey(device.getType())) {
                 deviceIdentifierMap.get(device.getType()).add(device.getDeviceIdentifier());
             } else {
-                    deviceIdentifierMap.put(device.getType(), Collections.singletonList(device.getDeviceIdentifier()));
+                deviceIdentifierMap.put(device.getType(),
+                        new ArrayList<>(Collections.singletonList(device.getDeviceIdentifier())));
                 DeviceManager deviceManager = this.getDeviceManager(device.getType());
                 if (deviceManager == null) {
-                        log.error("Device Manager associated with the device type '" + device.getType() +
+                    log.error("Device Manager associated with the device type '" + device.getType()
-                                "' is null. Therefore, not attempting method 'deleteDevice'");
+                            + "' is null. Therefore, not attempting method 'deleteDevice'");
                     return false;
                 }
                 deviceManagerMap.put(device.getType(), deviceManager);
@@ -651,6 +652,8 @@ public class DeviceManagementProviderServiceImpl implements DeviceManagementProv
         if (log.isDebugEnabled()) {
             log.debug("Permanently deleting the details of devices : " + validDeviceIdentifiers);
         }
+
+        try {
             DeviceManagementDAOFactory.beginTransaction();
             //deleting device from the core
             deviceDAO.deleteDevices(validDeviceIdentifiers, new ArrayList<>(deviceIds), enrollmentIds);