* test/integration: only run against 1 envoy version
These tests are slow enough that it seems unlikely that anyone is
running multiple versions locally. If someone wants to, a for loop
outside of run_test.sh should do the right thing.
Remove unused vars.
* Remove logic to iterate over test cases, run a single case
* Add a golang runner for integration tests
* Use build tags for envoy integration tests
And add junit-xml report
