Autogen python test config.

Feature request from developer, autogen python test config.

Bug:118442443

Test: $source build/envsetup.sh ; lunch
      $sed -i '/test_config/d' tools/acloud/Android.bp
      $make acloud_test
      $[ -f $ANDROID_HOST_OUT_TESTCASES/acloud_test/acloud_test.config ] && echo "Found" || echo "Not found"

Change-Id: I196230581b456afe03e67f9cd84c028d18ba08d9