Change MANIFEST.in to include python regression tests in tarball (#841)

* Change MANIFEST.in to include python regression tests in tarball

* Python tests need the testdata from the base tests directory
diff --git a/MANIFEST.in b/MANIFEST.in
index b7b8e72..ff8d600 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -12,6 +12,8 @@
 include python/bro.py
 include python/brotli.py
 include python/README.md
+include python/tests/*
 include README.md
 include setup.py
+include tests/testdata/*
 include c/tools/brotli.c