Initial struct definitions, jobspec parsing, validation, and conversion
between Nomad structs and API structs for multi-region deployments.

Allow a `/v1/jobs?all_namespaces=true` to list all jobs across all
namespaces.  The returned list is to contain a `Namespace` field
indicating the job namespace.

If ACL is enabled, the request token needs to be a management token or
have `namespace:list-jobs` capability on all existing namespaces.

updated ScalingEvent API to record "message string,error bool" instead
of confusing "reason,error *string"

Enable configuration of HTTP and gRPC endpoints which should be exposed by
the Connect sidecar proxy. This changeset is the first "non-magical" pass
that lays the groundwork for enabling Consul service checks for tasks
running in a network namespace because they are Connect-enabled. The changes
here provide for full configuration of the

  connect {
    sidecar_service {
      proxy {
        expose {
          paths = [{
		path = <exposed endpoint>
                protocol = <http or grpc>
                local_path_port = <local endpoint port>
                listener_port = <inbound mesh port>
	  }, ... ]
       }
    }
  }

stanza. Everything from `expose` and below is new, and partially implements
the precedent set by Consul:
  https://www.consul.io/docs/connect/registration/service-registration.html#expose-paths-configuration-reference

Combined with a task-group level network port-mapping in the form:

  port "exposeExample" { to = -1 }

it is now pos...

added ACL protection in Job.Scale
in Job.Scale, only perform a Job.Register if the Count was non-nil

Consul provides a feature of Service Definitions where the tags
associated with a service can be modified through the Catalog API,
overriding the value(s) configured in the agent's service configuration.

To enable this feature, the flag enable_tag_override must be configured
in the service definition.

Previously, Nomad did not allow configuring this flag, and thus the default
value of false was used. Now, it is configurable.

Because Nomad itself acts as a state machine around the the service definitions
of the tasks it manages, it's worth describing what happens when this feature
is enabled and why.

Consider the basic case where there is no Nomad, and your service is provided
to consul as a boring JSON file. The ultimate source of truth for the definition
of that service is the file, and is stored in the agent. Later, Consul performs
"anti-entropy" which synchronizes the Catalog (stored only the leaders). Then
with enable_tag_override=true, t...

This change provides an initial pass at setting up the configuration necessary to
enable use of Connect with Consul ACLs. Operators will be able to pass in a Consul
Token through `-consul-token` or `$CONSUL_TOKEN` in the `job run` and `job revert`
commands (similar to Vault tokens).

These values are not actually used yet in this changeset.

* adds meta object to service in job spec, sends it to consul

* adds tests for service meta

* fix tests

* adds docs

* better hashing for service meta, use helper for copying meta when registering service

* tried to be DRY, but looks like it would be more work to use the
helper function

Refactor all Consul structs into {api,structs}/services.go because
api/tasks.go didn't make sense anymore and structs/structs.go is
gigantic.

- updated region in job metadata that gets persisted to nomad datastore
- fixed many unrelated unit tests that used an invalid region value
(they previously passed because hcl wasn't getting picked up and
the job would default to global region)

Fixes Migrate to be initialized like RescheduleStrategy.

Fixes #5477

`api.MockJob` is a test utility, that's only used by `command/agent`
package.  This moves it to the package and removes it from the public
API.

Added CLI for evaluating job given ID, and modified client API for evaluate to take a request payload