The e2e framework instantiates clients for Nomad/Consul but the
provisioning of the actual Nomad cluster is left to Terraform. The
Terraform provisioning process uses `remote-exec` to deploy specific
versions of Nomad so that we don't have to bake an AMI every time we
want to test a new version. But Terraform treats the resulting
instances as immutable, so we can't use the same tooling to update the
version of Nomad in-place. This is a prerequisite for upgrade testing.
This changeset extends the e2e framework to provide the option of
deploying Nomad (and, in the future, Consul/Vault) with specific
versions to running infrastructure. This initial implementation is
focused on deploying to a single cluster via `ssh` (because that's our
current need), but provides interfaces to hook the test run at the
start of the run, the start of each suite, or the start of a given
test case.
Terraform work includes:
* provides Terraform output that written to JSON used by the framework
to configure provisioning via `terraform output provisioning`.
* provides Terraform output that can be used by test operators to
configure their shell via `$(terraform output environment)`
* drops `remote-exec` provisioning steps from Terraform
* makes changes to the deployment scripts to ensure they can be run
multiple times w/ different versions against the same host.
