client: wait for batched driver updates before registering nodes

Noticed that `detected drivers` log line was misleading - when a driver
doesn't fingerprint before timeout, their health status is empty string
`""` which we would mark as detected.

Now, we log all drivers along with their state to ease driver
fingerprint debugging.

I noticed that `watchNodeUpdates()` almost immediately after
`registerAndHeartbeat()` calls `retryRegisterNode()`, well after 5
seconds.

This call is unnecessary and made debugging a bit harder.  So here, we
ensure that we only re-register node for new node events, not for
initial registration.

Here we retain 0.8.7 behavior of waiting for driver fingerprints before
registering a node, with some timeout.  This is needed for system jobs,
as system job scheduling for node occur at node registration, and the
race might mean that a system job may not get placed on the node because
of missing drivers.

The timeout isn't strictly necessary, but raising it to 1 minute as it's
closer to indefinitely blocked than 1 second.  We need to keep the value
high enough to capture as much drivers/devices, but low enough that
doesn't risk blocking too long due to misbehaving plugin.

Fixes https://github.com/hashicorp/nomad/issues/5579

Add preemption related fields to AllocationListStub

Switch to pre-0.9 behaviour for handling volumes

docs: Clarify docker volume behaviour

In Nomad 0.9, we made volume driver handling the same for `""`, and
`"local"` volumes. Prior to Nomad 0.9 however these had slightly different
behaviour for relative paths and named volumes.

Prior to 0.9 the empty string would expand relative paths within the task
dir, and `"local"` volumes that are not absolute paths would be treated
as docker named volumes.

This commit reverts to the previous behaviour as follows:

| Nomad Version | Driver  |   Volume Spec    | Behaviour                 |
|-------------------------------------------------------------------------
| all           | ""      | testing:/testing | allocdir/testing          |
| 0.8.7         | "local" | testing:/testing | "testing" as named volume |
| 0.9.0         | "local" | testing:/testing | allocdir/testing          |
| 0.9.1         | "local" | testing:/testing | "testing" as named volume |

list singularity as a community driver

Fixes #5566 .

Fix a case where docker logging process may lock up nomad agent restart.

Looks like we have a case where docker logger is started even through logmon isn't. In such case, the fifo writer blocks indefinitely and because the open operation happens in the main goroutine, nomad agent blocks indefinitely.

This fixes the issue where the fifo open operation happens in goroutine instead of main goroutine.

We should follow up independently to ensure logmon <-> dockerlogger ordering and consider having task recovery happen in non-main goroutine with some sensible timeouts.

Signed-off-by: Eduardo Arango <eduardo@sylabs.io>

Signed-off-by: Eduardo Arango <eduardo@sylabs.io>

vault: fix renewal time

Renewal time was being calculated as 10s+Intn(lease-10s), so the renewal
time could be very rapid or within 1s of the deadline: [10s, lease)

This commit fixes the renewal time by calculating it as:

	(lease/2) +/- 10s

For a lease of 60s this means the renewal will occur in [20s, 40s).

client: simplify kill logic

api: fix migrate stanza initialization

docs: Add docs for nomad-alloc-restart

cli: add support for periodic force evaluation

Add `nomad alloc restart` and `nomad status -verbose`

Merge branch 'website_docs_singularity' of github.com:ArangoGutierrez/nomad into website_docs_singularity

Signed-off-by: Eduardo Arango <eduardo@sylabs.io>

resolves #3251