Fix the election was reset wrongly before failover epoch was obtained

[enjoy-binbin]

After #1009, we will reset the election when we received
a claim with an equal or higher epoch since a node can win
an election in the past.

But we need to consider the time before the node actually
obtains the failover_auth_epoch. The failover_auth_epoch
default is 0, so before the node actually get the failover
epoch, we might wrongly reset the election.

This is probably harmless, but will produce misleading log
output and may delay election by a cron cycle or beforesleep.
Now we will only reset the election when a node is actually
obtains the failover epoch.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.61%. Comparing base (50aae13) to head (c2d5d61).
Report is 40 commits behind head on unstable.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1339      +/-   ##
============================================
- Coverage     70.76%   70.61%   -0.16%     
============================================
  Files           116      116              
  Lines         63271    63281      +10     
============================================
- Hits          44776    44688      -88     
- Misses        18495    18593      +98     

Files with missing lines	Coverage Δ
src/cluster_legacy.c	86.30% <100.00%> (-0.22%)	⬇️

... and 14 files with indirect coverage changes