auto-t: throw exception if executable is missing

Certain tests may require external processes to work
(e.g. testNetconfig) and if missing the test will just hang until
the maximum test timeout. Check in start_process if the exe
actually exists and if not throw an exception.

tools/utils.py

@@ -34,6 +34,9 @@ class Process(subprocess.Popen):
 
 		logfile = args[0]
 
+		if not shutil.which(args[0]):
+			raise Exception("%s is not found on system" % args[0])
+
 		if Process.is_verbose(args[0], log=False):
 			self.verbose = True