add command pop_blocks

add new public method to Blockchain and update according to code review

update after review: better lock/unlock, try catch and coding style

src/daemon/rpc_command_executor.cpp

@@ -1967,4 +1967,31 @@ bool t_rpc_command_executor::sync_info()
     return true;
 }
 
+bool t_rpc_command_executor::pop_blocks(uint64_t num_blocks)
+{
+  cryptonote::COMMAND_RPC_POP_BLOCKS::request req;
+  cryptonote::COMMAND_RPC_POP_BLOCKS::response res;
+  std::string fail_message = "pop_blocks failed";
+
+  req.nblocks = num_blocks;
+  if (m_is_rpc)
+  {
+    if (!m_rpc_client->rpc_request(req, res, "/pop_blocks", fail_message.c_str()))
+    {
+      return true;
+    }
+  }
+  else
+  {
+    if (!m_rpc_server->on_pop_blocks(req, res) || res.status != CORE_RPC_STATUS_OK)
+    {
+      tools::fail_msg_writer() << make_error(fail_message, res.status);
+      return true;
+    }
+  }
+  tools::success_msg_writer() << "new height: " << res.height;
+
+  return true;
+}
+
 }// namespace daemonize