bpo-30871: Add test.pythoninfo (#3075)

* Add Lib/test/pythoninfo.py: script collecting various informations
  about Python to help debugging test failures.
* regrtest: remove sys.hash_info and sys.flags from header.
* Travis CI, Appveyor: run pythoninfo before tests
diff --git a/.travis.yml b/.travis.yml
index ba1e417..4c43124 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -60,6 +60,7 @@
             # Need a venv that can parse covered code.
             ./python -m venv venv
             ./venv/bin/python -m pip install -U coverage
+            ./venv/bin/python -m test.pythoninfo
       script:
         # Skip tests that re-run the entire test suite.
         - ./venv/bin/python -m coverage run --pylib -m test -uall,-cpu -x test_multiprocessing_fork -x test_multiprocessing_forkserver -x test_multiprocessing_spawn
@@ -87,6 +88,7 @@
         echo "$changes"
         exit 1
       fi
+      ./python -m test.pythoninfo
 
 script:
   # Using the built Python as patchcheck.py is built around the idea of using