Parallel targets support

[ttufts]

Finished implementing parallel target support, removed hardcoded target index 0 and added iterator cycling so that mutations are load leveled over all targets that are added.

[ttufts]

Ran unit tests, all related tests pass, failing on test_monitors.py but that doesn't seem to be related. Might be running something wrongly.

[SR4ven]

Sorry for the late review and thanks for the PR @ttufts!

I just tested the change with two targets and it seems that the test are now being sent to the targets in an alternating way.
Case 1 -> Target 1
Case 2 -> Target 2
Case 3 -> Target 1
Case 4 -> Target 2

When it should be like this:
Case 1 -> Target 1
Case 1 -> Target 2
Case 2 -> Target 1
Case 2 -> Target 2

We should also add some kind of info about the current target to the logging, so that it's clear which target is currently in use.

Additionally, we should give the constructor of Session an option for multiple targets in form of a list.
Also, I noticed, that calling Session.add_target() will not execute the following code that is currently only present in the constructor.

boofuzz/boofuzz/sessions.py

Lines 578 to 591 in 12ec28c

	if target is not None:
	def apply_options(monitor):
	monitor.set_options(crash_filename=self._crash_filename)
	return
	target.monitor_alive.append(apply_options)
	try:
	self.add_target(target)
	except exception.BoofuzzRpcError as e:
	self._fuzz_data_logger.log_error(str(e))
	raise

So monitors are not equally set up with both methods.