checker: keep the original database error in the error message (#276)

[csuzhangxc]

What problem does this PR solve?

cherry-pick #276

keep the original database error in the error message for checker.

What is changed and how it works?

use Error.Delegate to replace Error.Generate.

Check List

Tests

• Manual test (add detailed scripts or steps below)
  1. set a wrong password for DM-worker
  2. start-task
     the original error message is

     [code=26002:class=dm-master:scope=upstream:level=high] fail to initial checker: failed to open DSN root:***@127.0.0.1:3306\ngit.luolix.top/pingcap/dm/pkg/terror.(*Error).Generate\n\t/Users/zhangxc/gopath/src/github.com/pingcap/dm/pkg/terror/terror.go:232\ngit.luolix.top/pingcap/dm/checker.(*Checker).Init\n\t/Users/zhangxc/gopath/src/github.com/pingcap/dm/checker/checker.go:129\ngit.luolix.top/pingcap/dm/checker.CheckSyncConfig\n\t/Users/zhangxc/gopath/src/github.com/pingcap/dm/checker/cmd.go:50\ngit.luolix.top/pingcap/dm/dm/master.(*Server).generateSubTask\n\t/Users/zhangxc/gopath/src/github.com/pingcap/dm/dm/master/server.go:1847\ngit.luolix.top/pingcap/dm/dm/master.(*Server).StartTask\n\t/Users/zhangxc/gopath/src/github.com/pingcap/dm/dm/master/server.go:220\ngit.luolix.top/pingcap/dm/dm/pb._Master_StartTask_Handler\n\t/Users/zhangxc/gopath/src/github.com/pingcap/dm/dm/pb/dmmaster.pb.go:1530\ngoogle.golang.org/grpc.(*Server).processUnaryRPC\n\t/Users/zhangxc/gopath/pkg/mod/google.golang.org/grpc@v1.23.0/server.go:995\ngoogle.golang.org/grpc.(*Server).handleStream\n\t/Users/zhangxc/gopath/pkg/mod/google.golang.org/grpc@v1.23.0/server.go:1275\ngoogle.golang.org/grpc.(*Server).serveStreams.func1.1\n\t/Users/zhangxc/gopath/pkg/mod/google.golang.org/grpc@v1.23.0/server.go:710\nruntime.goexit\n\t/usr/local/go/src/runtime/asm_amd64.s:1337
     

     the error message now is

     [code=26002:class=dm-master:scope=upstream:level=high] fail to initial checker: failed to open DSN root:***@127.0.0.1:3306: Error 1045: Access denied for user 'root'@'172.18.0.1' (using password: YES)\ngit.luolix.top/pingcap/dm/pkg/terror.(*Error).Delegate\n\t/Users/zhangxc/gopath/src/github.com/pingcap/dm/pkg/terror/terror.go:267\ngit.luolix.top/pingcap/dm/checker.(*Checker).Init\n\t/Users/zhangxc/gopath/src/github.com/pingcap/dm/checker/checker.go:129\ngit.luolix.top/pingcap/dm/checker.CheckSyncConfig\n\t/Users/zhangxc/gopath/src/github.com/pingcap/dm/checker/cmd.go:50\ngit.luolix.top/pingcap/dm/dm/master.(*Server).generateSubTask\n\t/Users/zhangxc/gopath/src/github.com/pingcap/dm/dm/master/server.go:1847\ngit.luolix.top/pingcap/dm/dm/master.(*Server).StartTask\n\t/Users/zhangxc/gopath/src/github.com/pingcap/dm/dm/master/server.go:220\ngit.luolix.top/pingcap/dm/dm/pb._Master_StartTask_Handler\n\t/Users/zhangxc/gopath/src/github.com/pingcap/dm/dm/pb/dmmaster.pb.go:1530\ngoogle.golang.org/grpc.(*Server).processUnaryRPC\n\t/Users/zhangxc/gopath/pkg/mod/google.golang.org/grpc@v1.23.0/server.go:995\ngoogle.golang.org/grpc.(*Server).handleStream\n\t/Users/zhangxc/gopath/pkg/mod/google.golang.org/grpc@v1.23.0/server.go:1275\ngoogle.golang.org/grpc.(*Server).serveStreams.func1.1\n\t/Users/zhangxc/gopath/pkg/mod/google.golang.org/grpc@v1.23.0/server.go:710\nruntime.goexit\n\t/usr/local/go/src/runtime/asm_amd64.s:1337
     

Related changes

• Need to cherry-pick to the release branch

[codecov]

Codecov Report

Merging #278 into release-1.0 will increase coverage by 0.0542%.
The diff coverage is 0%.

@@                 Coverage Diff                 @@
##           release-1.0       #278        +/-   ##
===================================================
+ Coverage       60.004%   60.0582%   +0.0542%     
===================================================
  Files              134        134                
  Lines            14759      14759                
===================================================
+ Hits              8856       8864         +8     
+ Misses            5057       5049         -8     
  Partials           846        846

[csuzhangxc]

@amyangfei @WangXiangUSTC PTAL

[amyangfei]

LGTM

[WangXiangUSTC]

LGTM