All allocation stats are routable from the server

Convert all cpu and memory usage fields regardless of stated measured
fields, and handle swap fields

Fix a case where TotalTicks doesn't get serialized across executor grpc
calls.

Here, I opted to implicit add field, rather than explicitly mark it as a
measured field, because it's a derived field and to preserve 0.8
behavior where total ticks aren't explicitly marked as a measured field.

docker: restore pre-0.9 container names

As far as I can tell Nomad itself does not use the container name after
container creation, so this should be safe.

OP: https://groups.google.com/d/topic/nomad-tool/kYkyERfVRXE/discussion
v0.8.7 code: https://github.com/hashicorp/nomad/blob/v0.8.7/client/driver/docker.go#L1530-L1531

* Divest api/ package of deps elsewhere in the nomad repo.

This will allow making api/ a module without then pulling in the
external repo, leading to a package name conflict.

This required some migration of tests to an apitests/ folder (can be
moved anywhere as it has no deps on it). It also required some
duplication of code, notably some test helpers from api/ -> apitests/
and part (but not all) of testutil/ -> api/testutil/.

Once there's more separation and an e.g. sdk/ folder those can be
removed in favor of a dep on the sdk/ folder, provided the sdk/ folder
doesn't depend on api/ or /.

* Also remove consul dep from api/ package

* Fix stupid linters

* Some restructuring

docs: mention support for centos6 is dropped

Fix json parsing bug with plugins that don't provide args

This fixes a bug with JSON agent configuration parsing where the AST
for the plugin stanza had unnecessary flattening originating from hcl parsing
library. The workaround fixes the AST by popping off the flattened element and wrapping
it in a list. The workaround comes from similar code in terraform.

There were no existing test cases for json parsing so I added a few.

Use specific url prefix for metrics test

Also changed the output to show client node IP addresses

Fixup mixed tabs in script for Vagrantfile demo

This commit replaces a hard tab with two spaces to match the intendation
of the rest of the defined script

minor fixes to spread stanza documentation

tests: port pre-0.9 task env tests

I chose to make them more of integration tests since there's a lot more
plumbing involved. The internal implementation details of how we craft
task envs can now change and these tests will still properly assert the
task runtime environment is setup properly.

test: properly skip client state in beforeall

release: skip check step when cutting release

Now `prerelease` no longer requires linters

`make check` runs very intensive linters that slow and seem to behave
differently on different machines.

Linting is still a part of our CI and we shouldn't be cutting a release
when CI isn't green anyway.

client/logmon: restart log collection correctly when a task is restarted

Prometheus metrics for the e2e environment

Test state corruption