Fix testmodule for jhbuild autobuild

Fix testmodule for jhbuild autobuild

If the moduleset contains a TestModule, jhbuild autobuild dies

Traceback (most recent call last):
  File "/usr/local/bin/jhbuild", line 31, in <module>
    jhbuild.main.main(sys.argv[1:])
  File "/usr/local/jhbuild/jhbuild/main.py", line 136, in main
    rc = jhbuild.commands.run(command, config, args, help=lambda: print_help(parser))
  File "/usr/local/jhbuild/jhbuild/commands/__init__.py", line 123, in run
    return cmd.execute(config, args, help)
  File "/usr/local/jhbuild/jhbuild/commands/__init__.py", line 52, in execute
    return self.run(config, options, args, help)
  File "/usr/local/jhbuild/jhbuild/commands/autobuild.py", line 89, in run
    return build.build()
  File "/usr/local/jhbuild/jhbuild/frontends/buildscript.py", line 149, in build
    self.end_phase(module.name, phase, error)
  File "/usr/local/jhbuild/jhbuild/frontends/autobuild.py", line 259, in end_phase
    self.modules = jhbuild.moduleset.load_tests(self.config)
  File "/usr/local/jhbuild/jhbuild/moduleset.py", line 301, in load_tests
    if module.__class__ == testmodule.TestModule:
NameError: global name 'testmodule' is not defined