Bump go.etcd.io/etcd from 3.3.18+incompatilve to v0.5.0-alpha.5.0.20200306183522-221f0cc107cb

[gdbelvin]

Cherry-pick etcd to include this fix: etcd-io/etcd#11564

go get go.etcd.io/etcd@221f0cc107cb3497eeb20fb241e1bcafca2e9115

Fixes: #2044 and all other dependencies that transitively depend on grpc > v1.27.

Related:
etcd-io/etcd#11154
etcd-io/etcd#11477

We might want to wait on this PR until etcd cuts a new release.

[codecov]

Codecov Report

Merging #2064 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2064   +/-   ##
=======================================
  Coverage   58.93%   58.93%           
=======================================
  Files         115      115           
  Lines        9779     9779           
=======================================
  Hits         5763     5763           
  Misses       3513     3513           
  Partials      503      503

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[gdbelvin]

It looks like this also causes go get to revert to an older version of certificate-transparency-go.

This PR is blocked on

• etcd.io cutting 3.19.0
• certificate-transpraency-go depending on it ?
• updating Trillian's dependency on it.