Split E2E tests into separate packages based on provider, extract common functions into their own packages

This issue deals with organizing the structure of the e2e tests package (`test/e2e`) into a more modular format based on provider (`docker`, `vsphere`, `cloudstack`, etc.). This will allow us to apply tags to filter in/out the specific suite of tests that we want for each provider. PR #3475 addresses this.

Start in test/e2e and review PR #3475, which the issue identifies as addressing this work. Examine how the Docker, vSphere, and CloudStack tests are organized and where common functions are used. Done means provider-specific packages can be selected with tags and shared functions are extracted into their own packages.

Written by the indexing model from the issue text.