Fixed build file for service_only bootstrap

[devos50]

The build.py file expects the window arg to be set, however, when building with a service_only bootstrap, this variable is not set. This results in an error when building the private.mp3 resource.

[AndreMiras]

Thanks for the contribution. This actually rings the bell, I think I saw a similar update in the past.
Anyway it looks good, but the build is failing for an unknown reason. I'd like us to investigate before merging. It's probably not related to this PR, but we now have errors all over the place like:

==================================== ERRORS ====================================
_____________________ ERROR collecting tests/test_graph.py _____________________
ImportError while importing test module '/home/travis/build/kivy/python-for-android/tests/test_graph.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
tests/test_graph.py:1: in <module>
    from pythonforandroid.build import Context
E   ImportError: No module named pythonforandroid.build
____________________ ERROR collecting tests/test_logger.py _____________________
ImportError while importing test module '/home/travis/build/kivy/python-for-android/tests/test_logger.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
tests/test_logger.py:3: in <module>
    from pythonforandroid import logger
E   ImportError: No module named pythonforandroid
______________ ERROR collecting tests/test_pythonpackage_basic.py ______________
ImportError while importing test module '/home/travis/build/kivy/python-for-android/tests/test_pythonpackage_basic.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
tests/test_pythonpackage_basic.py:17: in <module>
    from pythonforandroid.pythonpackage import (
E   ImportError: No module named pythonforandroid.pythonpackage
____________________ ERROR collecting tests/test_recipe.py _____________________
ImportError while importing test module '/home/travis/build/kivy/python-for-android/tests/test_recipe.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
tests/test_recipe.py:5: in <module>
    from pythonforandroid.build import Context
E   ImportError: No module named pythonforandroid.build
________________ ERROR collecting tests/recipes/test_gevent.py _________________

https://travis-ci.org/kivy/python-for-android/builds/534106361

[devos50]

This actually rings the bell, I think I saw a similar update in the past.

Yes, it is part of an open PR (#1725) but I decided to create a separate PR since our software highly depends on the service_only bootstrap 👍 .

[AndreMiras]

That's the one indeed, thanks for sharing.
I'll try to take a look why the build is failing during the coming week so we can merge that PR

[AndreMiras]

Hi @devos50 the issue was fixed by @opacam in #1820 could you rebase your pull request on master?

[devos50]

@AndreMiras done 👍

[AndreMiras]

Thanks!

[AndreMiras]

Nice work, merged thanks!