Integration tests: Use testing.T logger through zap for grpc

[ptabor]

This finishes of unification of testing infrastructure for integration tests.

Now: RAFT + GRPC + per-etcd-member data are logged in consistent way through testing.T.

In case of test failure, the printed log contains all and only relevant information. It's very useful to understand root-causes of flakes.

[codecov-io]

Codecov Report

Merging #12781 (ee3182e) into master (e599f4a) will decrease coverage by 6.26%.
The diff coverage is 40.00%.

@@            Coverage Diff             @@
##           master   #12781      +/-   ##
==========================================
- Coverage   72.24%   65.97%   -6.27%     
==========================================
  Files         427      410      -17     
  Lines       33159    32692     -467     
==========================================
- Hits        23955    21568    -2387     
- Misses       7271     9205    +1934     
+ Partials     1933     1919      -14     

Flag	Coverage Δ
all	65.97% <40.00%> (-6.27%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
server/embed/config_logging.go	62.40% <25.00%> (+6.68%)	⬆️
server/etcdserver/raft.go	85.38% <100.00%> (ø)
raft/quorum/quorum.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/tlsutil/cipher_suites.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/transport/sockopt_unix.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/report/report.go	0.00% <0.00%> (-95.58%)	⬇️
pkg/srv/srv.go	0.00% <0.00%> (-87.94%)	⬇️
pkg/report/timeseries.go	0.00% <0.00%> (-86.77%)	⬇️
pkg/expect/expect.go	0.00% <0.00%> (-84.29%)	⬇️
pkg/osutil/interrupt_unix.go	0.00% <0.00%> (-82.61%)	⬇️
... and 111 more

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