Minor log fixes when failover auth denied due to slot epoch

[enjoy-binbin]

The old reqEpoch mainly refers to requestCurrentEpoch, see:

    if (requestCurrentEpoch < server.cluster->currentEpoch) {
        serverLog(LL_WARNING, "Failover auth denied to %.40s (%s): reqEpoch (%llu) < curEpoch(%llu)", node->name,
                  node->human_nodename, (unsigned long long)requestCurrentEpoch,
                  (unsigned long long)server.cluster->currentEpoch);
        return;
    }

And in here we refer to requestConfigEpoch, it's a bit misleading,
so change it to reqConfigEpoch to make it clear.

[enjoy-binbin]

I am struggling with the changes here. If it is not needed, you can use the review suggestion to remove it.

Suggested change

	serverLog(LL_NOTICE, "Starting a failover election for epoch %llu, node epoch is %llu",
	(unsigned long long)server.cluster->currentEpoch, (unsigned long long)nodeEpoch(myself));
	serverLog(LL_NOTICE, "Starting a failover election for epoch %llu.",
	(unsigned long long)server.cluster->currentEpoch);

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.78%. Comparing base (377ed22) to head (e161367).

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1341      +/-   ##
============================================
+ Coverage     70.77%   70.78%   +0.01%     
============================================
  Files           116      116              
  Lines         63280    63280              
============================================
+ Hits          44787    44794       +7     
+ Misses        18493    18486       -7     

Files with missing lines	Coverage Δ
src/cluster_legacy.c	86.33% <100.00%> (-0.29%)	⬇️

... and 8 files with indirect coverage changes

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