message: Fix TestMiExec.py
  r334215 changed the error message the tool prints for invalid thread
  arguments to -exec-next command. This adjust the test to match that.
diff: @@ -187,9 +187,9 @@ class MiExecTestCase(lldbmi_testcase.MiTestCaseBase):
  # Test that an invalid --thread is handled
  self.runCmd("-exec-next --thread 0")
  - self.expect("\^error,message=\"error: Thread index 0 is out of range")
  + self.expect("\^error,msg=\"Command 'exec-next'. Thread ID invalid")
  self.runCmd("-exec-next --thread 10")
  - self.expect("\^error,message=\"error: Thread index 10 is out of range")
  + self.expect("\^error,msg=\"Command 'exec-next'. Thread ID invalid")
  # Test that an invalid --frame is handled
  # FIXME: no error is returned
  