UI: Read the task event message from the DisplayMessage prop

Specify docker name in driver health messages

Allow to specify total memory on agent configuration

* Added extra debug logging; extended timeout; added jitter.

* small log changes

* increase timeout

* remove unneccessary uuid

drainer: reset index when new job registered

demo: give agents unique names

client: always mark exited sys/svc allocs as failed

drain: fix draining of system jobs

Create evals for system jobs when drain is unset

This PR creates evals for system jobs when:

* Drain is unset and mark eligible is true
* Eligibility is restored to the node

When restarts.attempts=0 was set in a jobspec a system or service alloc
that exited with 0 status would be marked as `completed` instead of
`failed`. Since system and service jobs are intended to run until
stopped or updated, they should always be marked as failed when they
exit even in cases where the exit code is 0.

Give demo agents unique names to improve `nomad node status` output.
Since the agents default to the hostname, they all had the same name
whether using the root or demo Vagrantfiles.

May want to bump this a bit more as the drain often completes amidst a
flurry of alloc updates.

Since the BatchJob helper had a different task group than the Alloc
helper, it was difficult to create a valid batch alloc.

System allocs should be drained when a node's deadline is hit or when
all other allocs on the node have stopped/migrated.

Properly format node event timestamps

Allow to set the total memory of an agent in its configuration file. This
can be used in case the automatic detection doesn't work or in specific
environments when memory overcommit (using swap for example) can be
desirable.

docs for delayed rescheduling options

Only track nodes if the conn is from the node

Fix alloc watcher snapshot streaming