HDDS-11742. don't reset SCM leadership metric to null on initilizing http server

[vtutrinov]

What changes were proposed in this pull request?

Reset SCM leadership metric to null only in case the leader is not defined earlier on initializing the RAFT server

When the SCM servers are in HA mode and start simultaneously leadership manages to settle down before the HTTP server starts. But the SCM main thread set the leadership to null with the suggestion the leadership is not defined yet, and the leadership will not be defined on prometheus metrics level:

bash-5.1$ for scm in {scm1,scm2,scm3}; do echo ${scm} && curl -s http://${scm}:9876/prom | grep scmha_metrics_scmha_leader_state ; done
scm1
# TYPE scmha_metrics_scmha_leader_state gauge
scmha_metrics_scmha_leader_state{nodeid="a8b30f45-58b0-4ab2-b52b-9aae232ccc10",hostname="e8121b3ddde2"} 0
scm2
# TYPE scmha_metrics_scmha_leader_state gauge
scmha_metrics_scmha_leader_state{nodeid="ae525b25-2774-4f91-9bbc-83884c1f472d",hostname="a467ff8d65d7"} 0
scm3
# TYPE scmha_metrics_scmha_leader_state gauge
scmha_metrics_scmha_leader_state{nodeid="a5d83fc8-7fe3-4d49-b8f6-159e411bf0fa",hostname="2ea45cb6b00a"} 0

The PR suggests resetting the leadership metric to null only in case the leader is not defined earlier on initializing the RAFT server. Also, the HA mini-cluster was rewritten to imitate the simultaneous start of the SCM servers in HA mode

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-11742

How was this patch tested?

With existing integration tests after making changes for the Ozone HA mini-cluster

[myskov]

Thanks @vtutrinov for the patch!

[myskov]

There's the following method for OM: OzoneManagerRatisServer.getLeaderId
maybe we should add the same for SCMRatisServer?