Adds Windows targets to the client/allocs metrics tests. Removes the
`allocstats` test, which covers less than these tests and is now
redundant.
Adds a firewall rule to our Windows instances so that the prometheus
server can scrape the Nomad HTTP API for metrics.
Refactor the metrics end-to-end tests so they can be run with our e2e
test framework. Runs fabio/prometheus and a collection of jobs that
will cause metrics to be measured. We then query Prometheus to ensure
we're publishing those allocation metrics and some metrics from the
clients as well.
Includes adding a placeholder for running the same tests on Windows.
The e2e test code is absolutely hideous and leaks processes and files
on disk. NomadAgent seems useful, but the clientstate e2e tests are very
messy and slow. The last test "Corrupt" is probably the most useful as
it explicitly corrupts the state file whereas the other tests attempt to
reproduce steps thought to cause corruption in earlier releases of
Nomad.
