fix incremental snapshot creation

Author: JoaoJandre

plugins/hypervisors/kvm/src/main/java/com/cloud/hypervisor/kvm/storage/KVMStorageProcessor.java

@@ -2093,7 +2093,22 @@ protected void rebaseSnapshot(SnapshotObjectTO snapshotObjectTO, KVMStoragePool
             QemuImg qemuImg = new QemuImg(wait);
             qemuImg.rebase(snapshotFile, parentSnapshotFile, PhysicalDiskFormat.QCOW2.toString(), false);
         } catch (LibvirtException | QemuImgException e) {
-            logger.error("Exception while rebasing incremental snapshot [{}] due to: [{}].", snapshotName, e.getMessage(), e);
+            if (!e.getMessage().contains("Is another process using the image")) {
+                logger.error("Exception while rebasing incremental snapshot [{}] due to: [{}].", snapshotName, e.getMessage(), e);
+                throw new CloudRuntimeException(e);
+            }
+            retryRebase(snapshotName, wait, e, snapshotFile, parentSnapshotFile);
+        }
+    }
+
+    private void retryRebase(String snapshotName, int wait, Exception e, QemuImgFile snapshotFile, QemuImgFile parentSnapshotFile) {
+        logger.warn("Libvirt still has not released the lock, will wait 60 seconds and try again later.");
+        try {
+            Thread.sleep(60*1000);
+            QemuImg qemuImg = new QemuImg(wait);
+            qemuImg.rebase(snapshotFile, parentSnapshotFile, PhysicalDiskFormat.QCOW2.toString(), false);
+        } catch (LibvirtException | QemuImgException | InterruptedException ex) {
+            logger.error("Unable to rebase snapshot [{}].", snapshotName, ex);
             throw new CloudRuntimeException(e);
         }
     }