jenkins-setup-build-env: actually run tests in the new buildserver VM

Oops, this has been failing, since it was running the build on the vm host,
not in the buildserver VM.

jenkins-setup-build-environment

@@ -79,6 +79,7 @@ else
 fi
 
 cd fdroiddata
+echo "build_server_always = True" > config.py
 
 if [ -z $ANDROID_HOME ]; then
     if [ -e ~/.android/bashrc ]; then