add NEU_REQRESP_GET_SELF_NODE_ID cmd
add get_datatags_table func
define neu_addt_str_t
fix compile warning
add magic number and check function in neu_plugin_common_t
1. Variable array serialization and deserialization support
2. Variable basic data type setting
3. Variable export function unit test
4. Integrate MQTT and Variable
5. Delete the work queue in the MQTT driver