graphd is always running even if waitForMetadReady is failed

[HarrisChu]

https://github.com/vesoft-inc/nebula/blob/master/src/graph/service/GraphService.cpp#L42

the behavior is different with storaged.

steps:

1. modify meta conf, --client_white_list=2.6.1
2. restart all the service.
3. login with nebula-console

actual result:

> nebula-console -addr 192.168.8.152 -port 9669 -u root -p nebula
2021/10/13 15:01:07 [INFO] connection pool is initialized successfully
2021/10/13 15:01:07 Fail to create a new session from connection pool, fail to authenticate, error: Bad username/password
panic: Fail to create a new session from connection pool, fail to authenticate, error: Bad username/password

root cause:

1. as modify client_white_list, meta client in graphd could not connect with metad.
2. but graphd don't exit, and client can connect to graphd.

more infomation:

1. nebula-graphd.INFO

Log line format: [IWEF]mmdd hh:mm:ss.uuuuuu threadid file:line] msg
I1013 07:00:47.399873 223843 GraphDaemon.cpp:125] Starting Graph HTTP Service
I1013 07:00:47.404433 223844 WebService.cpp:125] Web service started on HTTP[19669], HTTP2[19670]
I1013 07:00:47.404490 223843 GraphDaemon.cpp:139] Number of networking IO threads: 16
I1013 07:00:47.404502 223843 GraphDaemon.cpp:148] Number of worker threads: 16
I1013 07:00:47.404703 223843 MetaClient.cpp:58] Create meta client to "192.168.8.152":9559
E1013 07:00:49.411569 223843 MetaClient.cpp:95] Client verified failed: Meta client version(2.6.0) is not accepted, current meta client white list: 2.6.1.
W1013 07:00:49.411978 223843 GraphService.cpp:44] Failed to wait for meta service ready synchronously.
I1013 07:00:49.442003 223843 GraphDaemon.cpp:181] Starting nebula-graphd on 192.168.8.152:9669
I1013 07:00:50.266155 224028 GraphService.cpp:61] Authenticating user root from [::ffff:192.168.10.44]:50638
I1013 07:00:52.172744 224028 GraphService.cpp:61] Authenticating user root from [::ffff:192.168.10.44]:50643
I1013 07:01:07.316553 224028 GraphService.cpp:61] Authenticating user root from [::ffff:192.168.10.44]:50667

2. status

[vesoft@qa-tools nebula]$ ./scripts/nebula.service status all
[INFO] nebula-metad(e642c056): Running as 223737, Listening on 9559
[INFO] nebula-graphd(e642c056): Running as 223843, Listening on 9669
[INFO] nebula-storaged(e642c056): Exited

[HarrisChu]

expected:

graphd should be exited if metaclient is not ready.