*: Trace error

[zier-one]

What problem does this PR solve?

using errors.Trace() to trace most of errors in CDC

[suzaku]

LGTM

[codecov-io]

Codecov Report

Merging #176 into master will increase coverage by 0.01%.
The diff coverage is 9.67%.

@@            Coverage Diff             @@
##           master     #176      +/-   ##
==========================================
+ Coverage   49.53%   49.54%   +0.01%     
==========================================
  Files          50       50              
  Lines        4108     4109       +1     
==========================================
+ Hits         2035     2036       +1     
  Misses       1850     1850              
  Partials      223      223

Impacted Files	Coverage Δ
cdc/kv/etcd.go	29.46% <0%> (ø)	⬆️
cdc/roles/storage/etcd.go	75.42% <0%> (ø)	⬆️
cdc/capture.go	0% <0%> (ø)	⬆️
cdc/owner.go	33.08% <0%> (ø)	⬆️
cdc/puller/puller.go	0% <0%> (ø)	⬆️
cdc/kv/client.go	8.01% <0%> (ø)	⬆️
cdc/owner_operator.go	0% <0%> (ø)	⬆️
cdc/scheduler.go	52.86% <0%> (ø)	⬆️
cdc/sink/mysql.go	52.54% <22.22%> (+0.18%)	⬆️
cdc/txn/txn.go	78.78% <33.33%> (ø)	⬆️

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[amyangfei]

LGTM