*: test with "unparam", fix "v2v3" store stored get

[gyuho]

Fix #8068.
ref. #9064.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@e0b74d4). Click here to learn what that means.
The diff coverage is 71.15%.

@@            Coverage Diff            @@
##             master    #9712   +/-   ##
=========================================
  Coverage          ?   69.35%           
=========================================
  Files             ?      373           
  Lines             ?    35039           
  Branches          ?        0           
=========================================
  Hits              ?    24301           
  Misses            ?     8975           
  Partials          ?     1763

Impacted Files	Coverage Δ
pkg/transport/timeout_listener.go	80% <0%> (ø)
etcdmain/gateway.go	32.78% <0%> (ø)
etcdctl/ctlv3/command/watch_command.go	47.09% <0%> (ø)
etcdserver/api/v2v3/store.go	0% <0%> (ø)
etcdctl/ctlv3/command/del_command.go	70.73% <100%> (ø)
integration/bridge.go	71.75% <100%> (ø)
pkg/transport/listener.go	58.24% <100%> (ø)
etcdserver/v2auth/auth.go	72.33% <100%> (ø)
etcdctl/ctlv3/command/put_command.go	78.94% <100%> (ø)
etcdctl/ctlv3/command/get_command.go	77.27% <100%> (ø)
... and 7 more

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