Add epoch information to failover auth denied logs

[enjoy-binbin]

When failover deny to vote, sometimes due to network or
some blocking operations, the time of FAILOVER_AUTH_REQUEST
packet arrival is very uncertain. Since there is no epoch
information in these logs, it is hard to associate the log
with other logs.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 70.32%. Comparing base (59aa008) to head (9e23d3a).
Report is 95 commits behind head on unstable.

Files with missing lines	Patch %	Lines
src/cluster_legacy.c	33.33%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable     #816      +/-   ##
============================================
+ Coverage     70.18%   70.32%   +0.13%     
============================================
  Files           112      112              
  Lines         61311    61311              
============================================
+ Hits          43031    43116      +85     
+ Misses        18280    18195      -85     

Files with missing lines	Coverage Δ
src/cluster_legacy.c	85.59% <33.33%> (-0.07%)	⬇️

... and 12 files with indirect coverage changes

[zuiderkwast]

It's a good idea.