On Travis, put random data in ~/.torrc

.travis.yml

@@ -191,6 +191,9 @@ install:
   - python --version
   ## run stem tests if they are enabled.
   - if [[ "$TEST_STEM" != "" ]]; then pushd stem; python -c "from stem import stem; print(stem.__version__);"; git log -1; popd; fi
+  ## We don't want Tor tests to depends on default configuration file at
+  ## ~/.torrc. So we put some random bytes in there, to make sure it doesn't.
+  - dd ibs=1 count=1024 if=/dev/urandom > ~/.torrc
 
 script:
   # Skip test_rebind on macOS