tests: allow skipping load testing during int. tests. (#4168)
tests: allow skipping load testing during int. tests. (#4168)

Adds plumbing in `test.sh` to modify whether the `--load` argument is
provided to `test/integration-test.py`. Use `-e INT_SKIP_LOAD=true` with
`docker-compose run ... ./test.sh` to skip load generation.

bmw/boulder,jcjones/boulder,bmw/boulder,jcjones/boulder,jsha/boulder,letsencrypt/boulder,jsha/boulder,jcjones/boulder,letsencrypt/boulder,letsencrypt/boulder,jsha/boulder,jcjones/boulder,bmw/boulder