Upgrade etcd to 3.4.7

[gdbelvin]

Resolves CVE-2018-1098 CVE-2018-1099. etcd-io/etcd#10480

• The fix for GRPC v1.26 is delayed till etcd 3.5: CHANGELOG-3.5: update from #11564 etcd-io/etcd#11637
• Standardises on the new go.etcd.io/etcd import path
• Fix bbolt issues Fix unsafe pointer conversions caught by Go 1.14 checkptr etcd-io/bbolt#201
• Go module versioning is broken in etcd 3.4 go get error for 3.4.0 etcd-io/etcd#11154

The version number go.etcd.io/etcd v0.0.0-20200401174654-e694b7bb0875 was calculated with the following script, as suggested in etcd-io/etcd#11154

git clone --branch v3.4.7 https://github.com/etcd-io/etcd.git
cd etcd
echo -n v0.0.0-
TZ=UTC git --no-pager show \
  --quiet \
  --abbrev=12 \
  --date='format-local:%Y%m%d%H%M%S' \
  --format="%cd-%h"

[codecov]

Codecov Report

Merging #2089 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2089      +/-   ##
==========================================
- Coverage   58.94%   58.92%   -0.03%     
==========================================
  Files         115      115              
  Lines        9778     9778              
==========================================
- Hits         5764     5762       -2     
- Misses       3511     3513       +2     
  Partials      503      503              

Impacted Files	Coverage Δ
quota/etcd/etcdqm/etcdqm.go	92.59% <ø> (ø)
quota/etcd/quotaapi/quota_server.go	93.79% <ø> (ø)
quota/etcd/storage/quota_storage.go	84.15% <ø> (ø)
util/election2/etcd/election.go	75.00% <ø> (ø)
log/operation_manager.go	86.97% <0.00%> (-0.94%)	⬇️

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[gdbelvin]

@googlebot recheck