When a client is running against an old server (e.g. running 0.8),
`alloc.AllocatedResources` may be nil, and we need to check the
deprecated `alloc.TaskResources` instead.

Fixes https://github.com/hashicorp/nomad/issues/5810

Fix a panic related to updating alloc taskgroups

Alloc runner already tracks tasks associated with alloc.  Here, we
become defensive by relying on the alloc runner tracked tasks, rather
than depend on server never updating the job unexpectedly.

When an alloc is stopped, test that we don't update the job found in
alloc with new job  that is no longer relevent for this alloc.

It would be preferable to only generate these for UI PRs but Netlify appears to
not have that flexibility. I tried setting up manual deployments in a Travis
environment but gave up the experiment; it could probably eventually work if
deployment failures become a nuisance.

Only preempt for network when there is a network

When examining preemption for networks, only consider allocs that have
networks.

Fixes https://github.com/hashicorp/nomad/issues/5793

flaky e2e test

tests: Migrated allocs aren't lost

Fix `TestServiceSched_NodeDown` for checking that the migrated allocs
are actually marked to be stopped.

The boolean logic in test made it skip actually checking client status
as long as desired status was stop.

Here, we mark some jobs for migration while leaving others as running,
and we check that lost flag is only set for non-migrated allocs.

Fix a website link under `Runtime Environment`

Under the `Network-related Variables` the `NOMAD_HOST_PORT_<label>` has
a incorrect link.

Proposing new tfvars with additional inline docs

More test fixes

set node.StatusUpdatedAt in raft

Fix restart attempts of `restart` stanza in `delay` mode.

Revert 0.9.2 release super script tags

nomad: disable service+batch preemption by default

Add Enterprise docs for Preemption

Enterprise only.

Disable preemption for service and batch jobs by default.

Maintain backward compatibility in a x.y.Z release. Consider switching
the default for new clusters in the future.

client config flag to disable remote exec