elb_target/test: use 2nd venv

We pin the botocore version to avoid long list of download and save
time.

In order to keep the original ansible venv intact, we install
the specific boto version in a dedicated venv that with expose
to ansible with ansible_python_interpreter. This way we avoid
some conflict between ansible's dep and boto.

e.g: https://f73e17188c1e5a04acad-2f383edc1ebee1550897a1656739ef36.ssl.cf1.rackcdn.com/634/c7b79a3aeefd78a53e7afe854db0f9b673106f3f/check/ansible-test-cloud-integration-aws-py36_1/85f5ba0/job-output.txt

tests/integration/targets/elb_target/runme.sh

@@ -1,13 +1,13 @@
 #!/usr/bin/env bash
 
 set -eux
-
+unset PYTHONPATH
 # Test graceful failure for older versions of botocore
-source virtualenv.sh
-pip install 'botocore<=1.7.1' boto3
-ansible-playbook -i ../../inventory -v playbooks/version_fail.yml "$@"
+python3 -mvenv --clear _venv
+_venv/bin/pip install 'botocore==1.7.0' 'boto3==1.4.7' boto3
+ansible-playbook -i ../../inventory -v playbooks/version_fail.yml -e ansible_python_interpreter=$(pwd)/_venv/bin/python "$@"
 
 # Run full test suite
-source virtualenv.sh
-pip install 'botocore' 'boto3>=1.16.57'
-ansible-playbook -i ../../inventory -v playbooks/full_test.yml "$@"
+python3 -mvenv --clear _venv
+_venv/bin/pip install 'botocore' 'boto3>=1.16.57' boto3
+ansible-playbook -i ../../inventory -v playbooks/full_test.yml -e ansible_python_interpreter=$(pwd)/_venv/bin/python "$@"