* vault: configure user agent on Nomad vault clients
This PR attempts to set the User-Agent header on each Vault API client
created by Nomad. Still need to figure a way to set User-Agent on the
Vault client created internally by consul-template.
* vault: fixup find-and-replace gone awry
Our E2E "framework" has a bunch of features around test discovery and
standing up infra that were never completed or fully used, and we
ended up building out a large test suite that ignored all that in lieu
of Terraform-provided infrastructure for the last couple years.
This changeset is a proposal (and demonstration) for gradually
migrating our E2E tests off the framework code so that developers can
write fairly ordinary golang stdlib testing tests.
