Go 1.19 will forecefully format all your doc strings. To get this
out of the way, here is one big commit with all the changes gofmt
wants to make.

This PR introduces support for using Nomad on systems with cgroups v2 [1]
enabled as the cgroups controller mounted on /sys/fs/cgroups. Newer Linux
distros like Ubuntu 21.10 are shipping with cgroups v2 only, causing problems
for Nomad users.

Nomad mostly "just works" with cgroups v2 due to the indirection via libcontainer,
but not so for managing cpuset cgroups. Before, Nomad has been making use of
a feature in v1 where a PID could be a member of more than one cgroup. In v2
this is no longer possible, and so the logic around computing cpuset values
must be modified. When Nomad detects v2, it manages cpuset values in-process,
rather than making use of cgroup heirarchy inheritence via shared/reserved
parents.

Nomad will only activate the v2 logic when it detects cgroups2 is mounted at
/sys/fs/cgroups. This means on systems running in hybrid mode with cgroups2
mounted at /sys/fs/cgroups/unified (as is typical) Nomad will continue to
use the v1 logic, and should operat...

* driver: fix integer conversion error

The shared executor incorrectly parsed the user's group into int32 and
then cast to uint32 without bounds checking. This is harmless because
an out-of-bounds gid will throw an error later, but it triggers
security and code quality scans. Parse directly to uint32 so that we
get correct error handling.

* helper: fix integer conversion error

The autopilot flags helper incorrectly parses a uint64 to a uint which
is machine specific size. Although we don't have 32-bit builds, this
sets off security and code quality scaans. Parse to the machine sized
uint.

* driver: restrict bounds of port map

The plugin server doesn't constrain the maximum integer for port
maps. This could result in a user-visible misconfiguration, but it
also triggers security and code quality scans. Restrict the bounds
before casting to int32 and return an error.

* cpuset: restrict upper bounds of cpuset values

Our cpuset configuration expects values in the range of uint16 to
match the expectations set by the kernel, but we don't constrain the
values before downcasting. An underflow could lead to allocations
failing on the client rather than being caught earlier. This also make
security and code quality scanners happy.

* http: fix integer downcast for per_page parameter

The parser for the `per_page` query parameter downcasts to int32
without bounds checking. This could result in underflow and
nonsensical paging, but there's no server-side consequences for
this. Fixing this will silence some security and code quality scanners
though.

This PR switches the Nomad repository from using govendor to Go modules
for managing dependencies. Aspects of the Nomad workflow remain pretty
much the same. The usual Makefile targets should continue to work as
they always did. The API submodule simply defers to the parent Nomad
version on the repository, keeping the semantics of API versioning that
currently exists.