Direct grpc logs to Zap logger

[yurishkuro]

Resolves #1602, supersedes #1330.

Sample output:

{"level":"info","ts":1560530693.131958,"caller":"grpc/clientconn.go:242","msg":"parsed scheme: \"\"","system":"grpc","grpc_log":true}
{"level":"info","ts":1560530693.1319869,"caller":"grpc/clientconn.go:248","msg":"scheme \"\" not registered, fallback to default scheme","system":"grpc","grpc_log":true}
{"level":"info","ts":1560530693.132017,"caller":"grpc/resolver_conn_wrapper.go:113","msg":"ccResolverWrapper: sending update to cc: {[{127.0.0.1:14250 0  <nil>}] }","system":"grpc","grpc_log":true}
{"level":"info","ts":1560530693.132215,"caller":"base/balancer.go:76","msg":"base.baseBalancer: got new resolver state: {[{127.0.0.1:14250 0  <nil>}] }","system":"grpc","grpc_log":true}
{"level":"info","ts":1560530693.1323001,"caller":"base/balancer.go:130","msg":"base.baseBalancer: handle SubConn state change: 0xc000256040, CONNECTING","system":"grpc","grpc_log":true}
{"level":"info","ts":1560530693.132832,"caller":"grpc/clientconn.go:1139","msg":"grpc: addrConn.createTransport failed to connect to {127.0.0.1:14250 0  <nil>}. Err :connection error: desc = \"transport: Error while dialing dial tcp 127.0.0.1:14250: connect: connection refused\". Reconnecting...","system":"grpc","grpc_log":true}
{"level":"info","ts":1560530693.132919,"caller":"base/balancer.go:130","msg":"base.baseBalancer: handle SubConn state change: 0xc000256040, TRANSIENT_FAILURE","system":"grpc","grpc_log":true}

[codecov]

Codecov Report

Merging #1606 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1606   +/-   ##
=======================================
  Coverage   98.81%   98.81%           
=======================================
  Files         191      191           
  Lines        9162     9162           
=======================================
  Hits         9053     9053           
  Misses         85       85           
  Partials       24       24

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