plugin/health: Don't go lameduck when reloading

[chrisohaver]

Signed-off-by: Chris O'Haver cohaver@infoblox.com

1. Why is this pull request needed and what does it do?

When reloading health, don't pause for lameduck duration. Only go into lameduck mode on FinalShutdown.
During a reload, going into lameduck just delays the loading of the new config, and during the lameduck sleep, the old config is still served.

The new function OnReload is a copy of OnFinalShutdown with the lameduck pause removed.

2. Which issues (if any) are related?

Related to #5471

3. Which documentation changes (if any) need to be made?

4. Does this introduce a backward incompatible change or deprecation?

[codecov-commenter]

Codecov Report

Merging #5472 (3d829d5) into master (93c57b6) will increase coverage by 1.42%.
The diff coverage is 58.50%.

@@            Coverage Diff             @@
##           master    #5472      +/-   ##
==========================================
+ Coverage   55.70%   57.12%   +1.42%     
==========================================
  Files         224      238      +14     
  Lines       10016    15015    +4999     
==========================================
+ Hits         5579     8577    +2998     
- Misses       3978     5918    +1940     
- Partials      459      520      +61     

Impacted Files	Coverage Δ
core/dnsserver/address.go	100.00% <ø> (ø)
core/dnsserver/config.go	0.00% <ø> (ø)
core/dnsserver/onstartup.go	0.00% <0.00%> (ø)
core/dnsserver/server_grpc.go	8.16% <0.00%> (+2.10%)	⬆️
plugin/auto/auto.go	0.00% <0.00%> (ø)
plugin/auto/zone.go	78.94% <ø> (+0.68%)	⬆️
plugin/azure/azure.go	10.61% <0.00%> (-0.57%)	⬇️
plugin/backend_lookup.go	0.00% <0.00%> (ø)
plugin/bind/bind.go	50.00% <0.00%> (-50.00%)	⬇️
plugin/bufsize/bufsize.go	100.00% <ø> (ø)
... and 312 more

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