message: Fix TestMultithreaded when there's no debugserver specified
  r325858 was bogus and would error out with a KeyError when --server
  was not passed to dotest.py.
diff: @@ -101,7 +101,7 @@ class SBBreakpointCallbackCase(TestBase):
  exe = [test_exe, self.getBuildArtifact(self.inferior)]
  env = {self.dylibPath: self.getLLDBLibraryEnvVal()}
  - if os.environ['LLDB_DEBUGSERVER_PATH']:
  + if 'LLDB_DEBUGSERVER_PATH' in os.environ:
  env['LLDB_DEBUGSERVER_PATH'] = os.environ['LLDB_DEBUGSERVER_PATH']
  if self.TraceOn():
  print("Running test %s" % " ".join(exe))
  