Add capabilities to the LaunchRequest proto so that the
capabilities set actually gets plumbed all the way through
to task launch.

Looks like we no longer need a package.

The error output being checked depends on the linux caps supported
by the particular operating system. Fix these test cases to just
check that an error did occur.

Update docs for allow_caps, cap_add, cap_drop in exec/java/docker driver
pages. Also update upgrade guide with guidance on new default linux
capabilities for exec and java drivers.

This changeset does not introduce any functional change for the
docker driver, but rather cleans up the implementation around
computing configured capabilities by re-using code written for
the exec/java task drivers.

Enable setting allow_caps on the java task driver plugin, along
with the associated cap_add and cap_drop options in java task
configuration.

This PR enables setting allow_caps on the exec driver
plugin configuration, as well as cap_add and cap_drop in
exec task configuration. These options replicate the
functionality already present in the docker task driver.

Important: this change also reduces the default set of
capabilities enabled by the exec driver to match the
default set enabled by the docker driver. Until v1.0.5
the exec task driver would enable all capabilities supported
by the operating system. v1.0.5 removed NET_RAW from that
list of default capabilities, but left may others which
could potentially also be leveraged by compromised tasks.

Important: the "root" user is still special cased when
used with the exec driver. Older versions of Nomad enabled
enabled all capabilities supported by the operating system
for tasks set with the root user. To maintain compatibility
with existing clusters we continue supporting this "feature",
however we maintain support for the legacy set of c...

Remote Task Driver docs

Co-authored-by: Seth Hoenig <shoenig@hashicorp.com>

add a section about memory oversubscription
Co-authored-by: Tim Gross <tgross@hashicorp.com>

This closes #10513, thanks to @bastelfreak for the report.
GET /status/leader returns an IPv6 host with square brackets
around the IP address as expected, but the rpcAddr property
on the agent model does not.

This fixes rpcAddr, updates the Mirage /status/leader mock
to properly format an IPv6 host, and changes the agent
factory to sometimes produce IPv6 addresses.

I added a formatHost utility function to centralise the
conditional square bracket-wrapping that would have
otherwise been further scattered around.

website: update 1.1.0-beta1 to 1.1.0-rc1

This conditionally includes a region query parameter when
opening the exec socket.

The `capacity` block was removed during implementation in lieu of the
`capacity_max` and `capacity_min` fields, but it wasn't removed from the
example in the documentation.

minor: update 'Cloudflare' capitalization

update website to Nomad 1.0.5

drivers/docker+exec+java: disable net_raw capability by default

The default Linux Capabilities set enabled by the docker, exec, and
java task drivers includes CAP_NET_RAW (for making ping just work),
which has the side affect of opening an ARP DoS/MiTM attack between
tasks using bridge networking on the same host network.

https://docs.docker.com/engine/reference/run/#runtime-privilege-and-linux-capabilities

This PR disables CAP_NET_RAW for the docker, exec, and java task
drivers. The previous behavior can be restored for docker using the
allow_caps docker plugin configuration option.

A future version of nomad will enable similar configurability for the
exec and java task drivers.

* check and return error from parsing var-files

* changelog entry for 1.1.0 and 1.0.5

Co-authored-by: Mahmood Ali <mahmood@hashicorp.com>

Enable memory oversubscription for the oversubscription tests.

* docs: restructure autoscaling plugins menu

* docs: add autoscaling threshold strategy (#10535)