Also display the output and error output of a failed command

[teemperor]

Summary

Instead of just printing the current "False is not True, ..." message when we
fail to run a certain command, this patch also adds the actual command output or
error output that we received to the assertion message.

packages/Python/lldbsuite/test/lldbtest.py

def runCmd(self, cmd, msg=None, check=True, trace=False, inHistory=False):
                 break
             elif running:
                 # For process launch, wait some time before possible next try.
                 time.sleep(self.timeWaitNextLaunch)
                 with recording(self, trace) as sbuf:
                     print("Command '" + cmd + "' failed!", file=sbuf)
 
         if check:
+            output = ""
+            if self.res.GetOutput():
+              output += "\nCommand output:\n" + self.res.GetOutput()
+            if self.res.GetError():
+              output += "\nError output:\n" + self.res.GetError()
             self.assertTrue(self.res.Succeeded(),
-                            msg if msg else CMD_MSG(cmd))
+                            msg if (msg + output) else CMD_MSG(cmd + output))
 
     def match(
             self,
             str,
             patterns,
             msg=None,
             trace=False,
             error=False,