generic-experiment: generalize serial-output monitoring

The generic-experiment now learned to record and compare output on an
arbitrary serial port.  Using Bochs' port 0xe9 hack (parameter
--e9-file) is kept for compatibility reasons.

Change-Id: I5b1aa02d244e8b474919e1bdf043e523ea0e4f45

src/experiments/generic-tracing/experiment.hpp

@@ -28,8 +28,6 @@ class GenericTracing : public fail::ExperimentFlow {
 	fail::guest_address_t serial_port;
 	std::string serial_file;
 
-	std::string e9_file;
-
 	fail::Logger m_log;
 	fail::ElfReader *m_elf;