* jobspec: breakup parse.go into smaller files

* add sidecar_task parsing to jobspec and api

* jobspec: combine service parsing logic for task and group service stanzas

* api: use slice of ConsulUpstream values instead of pointers

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

Adds a network stanza and additional options to the task group level
in prep for allowing shared networking between tasks of an alloc.

IOPS have been modelled as a resource since Nomad 0.1 but has never
actually been detected and there is no plan in the short term to add
detection. This is because IOPS is a bit simplistic of a unit to define
the performance requirements from the underlying storage system. In its
current state it adds unnecessary confusion and can be removed without
impacting any users. This PR leaves IOPS defined at the jobspec parsing
level and in the api/ resources since these are the two public uses of
the field. These should be considered deprecated and only exist to allow
users to stop using them during the Nomad 0.9.x release. In the future,
there should be no expectation that the field will exist.

Needs to be more like http.

There was a bug in jobspec parsing, a bug in CheckRestart merging, and a
bug in CheckRestart canonicalization. All are now tested.

Fixes #3380

Adds address_mode to checks (but no auto) and allows services and checks
to set literal port numbers when using address_mode=driver.

This allows SDNs, overlays, etc to advertise internal and host addresses
as well as do checks against either.

add conversion for KillSignal for api/struct representation of task

Fixes #2441

Defaults to 0 (no delay) for backward compat and because this feature
should be opt-in.

This PR allows a template to specify the Vault grace duration.

Fixes https://github.com/hashicorp/nomad/issues/2922