Logrus instrumentation hook

[tonyredondo]

Closes #47

This PR contains a logrus hook implementation to write the logs in the span of the given context.

Usage

	ctx := scopeagent.GetContextFromTest(t).   // Gets the test context

	logger := logrus.New()
	logger.SetLevel(logrus.TraceLevel)
	logger.SetReportCaller(true)   // Allow to report the file and line number in the log event source
	AddScopeHook(logger)  // Adds the scope hook into the logros logger

	logger.WithContext(ctx).WithField("Data", "Value").Error("Error message")
	logger.WithContext(ctx).WithField("Data", "Value").Warn("Warning message")
	logger.WithContext(ctx).WithField("Data", "Value").Info("Info message")
	logger.WithContext(ctx).WithField("Data", "Value").Debug("Debug message")
	logger.WithContext(ctx).WithField("Data", "Value").Trace("Trace message")

Results

[drodriguezhdez]

Awesome @tonyredondo

I have a question: Can we have detect if the scope Hook was added before? To avoid adding several times.

I'm experiencing an issue in docker/distribution repo due to logrus.StandardLogger() returns a singleton, if the docker app is initialized several times, the hook is added those times with the following result:

[tonyredondo]

Mmm ok, I’ll make the change.

[tonyredondo]

Sorry for the delay, I've added a helper function for the problem you told me:

https://github.com/undefinedlabs/scope-go-agent/blob/logrus-support/instrumentation/logrus/hook.go#L24-L35

Just call it like:

AddScopeHook(logger)  // Adds the scope hook into the logros logger

[tonyredondo]

@drodriguezhdez

[drodriguezhdez]

awesome. Thanks @tonyredondo !