etcdserver, embed, integration: don't use pointer for ServerConfig

[heyitsanthony]

ServerConfig is owned by etdcserver and unshared, so don't pass or store by
pointer. Also removes duplicated field 'snapCount'.

[gyuho]

lgtm. thanks!

[gyuho]

@xiang90 https://github.com/kubernetes/kubernetes/blob/master/test/e2e_node/services/etcd.go#L90

Tagging this in release note, as well.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@066062a). Click here to learn what that means.
The diff coverage is 100%.

@@           Coverage Diff            @@
##             master   #7909   +/-   ##
========================================
  Coverage          ?   75.9%           
========================================
  Files             ?     332           
  Lines             ?   26315           
  Branches          ?       0           
========================================
  Hits              ?   19974           
  Misses            ?    4915           
  Partials          ?    1426

Impacted Files	Coverage Δ
embed/etcd.go	73.33% <100%> (ø)
integration/cluster.go	85.54% <100%> (ø)
etcdserver/raft.go	87.87% <100%> (ø)
etcdserver/server.go	80.99% <100%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 066062a...d433067. Read the comment docs.

[xiang90]

@heyitsanthony Look good to me.

One potential issue: InitialPeerURLsMap types.URLsMap is still a pointer type. So we are still not 100% safe. We do not try to change that field though.

[xiang90]

@heyitsanthony shall we get this merged?