license_script.sh calls pip install/uninstall in local env

File is: https://github.com/apache/beam/blob/master/sdks/java/container/license_scripts/license_script.sh

The problem is with the code that does pip install and uninstall.
1. It is not okay to modify the local environment.
2. Running this script in parallel with itself (on Jenkins) has a chance to cause a race.

The solution is to use a tox environment to run this script in. Tox will take care of creating a virtualenv with the required dependencies.