checker: keep the original database error in the error message

[csuzhangxc]

What problem does this PR solve?

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 #276 into master will increase coverage by 0.0474%.
The diff coverage is 0%.

@@               Coverage Diff               @@
##            master       #276        +/-   ##
===============================================
+ Coverage   60.004%   60.0514%   +0.0474%     
===============================================
  Files          134        134                
  Lines        14759      14759                
===============================================
+ Hits          8856       8863         +7     
+ Misses        5057       5052         -5     
+ Partials       846        844         -2

[csuzhangxc]

@amyangfei @WangXiangUSTC PTAL

[WangXiangUSTC]

LGTM

[amyangfei]

LGTM