Add minimal E2E testing

[gzurl]

A minimal E2E (end-to-end) testing would be using the demo container but with the mod_wasm.so and libwasm_runtime.so libraries built with the new code.

The test could be as simple as executing a curl over an endpoint served by the Wasm module in Apache and checking for its result.

The 'PrettyFy' WebApp could be a nice target since it requires the Python interpreter as the Wasm module: curl -vvv http://127.0.0.1:8080/wasm-module?file=search_word_count.py

Also, running the Apache Benchmark tool (in httpd/dist/bin) with a few tests in parallel could help to identify potential problems with the mutexes: ./ab -n 100 -c 10 http://192.168.64.2:8080/wasm-module?file=search_word_count.py

[gzurl]

Probably, a more convenient E2E test could be to run the "Hello Wasm!" example which doesn't require any runtime such as Python.