add missing requirements-pypy3.txt

After ce7b8dbf42de27eddd6e76b096c57d7f1abe845c all travis-ci jobs are
failing the pypy3 tests with `Could not open requirements file: [Errno 2] No such file or directory: 'requirements-pypy3.txt'`
Merge pull request #223 from dnozay/pypy3

add missing requirements-pypy3.txt
Add support for properties in junit xml.

jenkins junit xsd supports `<properties>` under `<testsuite>`.
This change allows the plugin to be configured to load those properties from
a json file (dictionary with key-value pairs); which you have to opt-in for by
specifying `test_properties` in the configuration.