Add 'verbose' option to logging minimum information (#275)

This change address #274 to add 'verbose option which outputs
minimum information (for usual runs with a bit information than
'error').

logging/logging_test.go

@@ -50,6 +50,8 @@ var _ = Describe("logging operations", func() {
 		Expect(loggingLevel).To(Equal(DebugLevel))
 		SetLogLevel("Error")
 		Expect(loggingLevel).To(Equal(ErrorLevel))
+		SetLogLevel("VERbose")
+		Expect(loggingLevel).To(Equal(VerboseLevel))
 		SetLogLevel("PANIC")
 		Expect(loggingLevel).To(Equal(PanicLevel))
 	})