* terror: print the stack in terror.Log()
In TiDB, terror.Log(err) is called when we expect the error to be nil
and get rid of the annoying golint check.
Sometimes the error is not nil as expected, so it's better to print the
stack to find why
* go fmt
* address comment
* address comment
* terror: replace sirupsen/logrus by pingcap/log
also fixed test failure on Windows
* circle.yml: restrict test parallelism in integration tests
also, stop verifying parser.go and code format in the integration tests...
those steps are redundant.
* codecov: add codecov.yml, based on pingcap/tidb#9618
Co-authored-by: tiancaiamao <tiancaiamao@gmail.com>