client: Fix double runs of the block execution (ethereumjs#2730)

* client: Fix double runs of the block execution

* fix comment

* clear cache is the vmhead not at parent stateroot

* run iterator inside the runwithlock to prevent entanglement with runWithoutSetHead or setHead

* fix lint

Author: g11tech

packages/blockchain/src/types.ts

@@ -62,6 +62,14 @@ export interface BlockchainInterface {
    */
   getIteratorHead?(name?: string): Promise<Block>
 
+  /**
+   * Set header hash of a certain `tag`.
+   * When calling the iterator, the iterator will start running the first child block after the header hash currently stored.
+   * @param tag - The tag to save the headHash to
+   * @param headHash - The head hash to save
+   */
+  setIteratorHead(tag: string, headHash: Uint8Array): Promise<void>
+
   /**
    * Gets total difficulty for a block specified by hash and number
    */