feat(security): receive mechanisms which are supported by server_negotiation

[levy5307]

In pr #588 , server_negotiation receives SASL_LIST_MECHANISMS request, and reply the mechanism that it supports. This pr is implemented to handle the SASL_LIST_MECHANISMS_RESP to get the mechanism supported by server_negotiation. And then select a mechanism which is supported by both client_negotiation and server_negotiation.

 negotiation process:

                                                  client                             server
                                                     |---    SASL_LIST_MECHANISMS     -->|
                                                     |<--  SASL_LIST_MECHANISMS_RESP  ---|
                                                     |---   SASL_SELECT_MECHANISMS   --->|
                                                     |<-- SASL_SELECT_MECHANISMS_RESP ---|
                                                     |                                   |
                                                     |------     SASL_INITIATE    ------>|
                                                     |                                   |
                                                     |<----      SASL_CHALLENGE     -----|
                                                     |-----       SASL_RESPONSE     ---->|
                                                     |                                   |
                                                     |               .....               |
                                                     |                                   |
                                                     |<----      SASL_CHALLENGE     -----|
                                                     |-----       SASL_RESPONSE     ---->|
                                                     |                                   |        (authentication will succeed
                                                     |                                   |        if all chanllenges passed)
                                                     | <---         SASL_SUCC       -----|
    (client won't response                           |                                   |
     if servers says ok)                             |                                   |
                                                     | ----          RPC_CALL       ---> |
                                                     | <---          RPC_RESP        ----|

New configuration added

[security]
+  mandatory_auth = false