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.
This change adds Darwin and FreeBSD C code of gopsutil library, that is
needed for these platforms. `shirou/gopsutil` uses some C code that
isn't in a go package, so don't get vendored automatically.
Previously used `github.com/shirou/gopsutil`[1], used some GPL code [2].
This was somewhat unintentional, and was addressed later [3].
Due to being late in the cycle of Nomad release when this is noticed,
and time elapsed since we updated the dependency, we want to be
conservative in our package updates.
As such, we opted to go with forking the repo to use the previously used
version with the GPL removal code commit, done in [4].
[1] 5776ff9c7c
[2] 5776ff9c7c/host/include/smc.c
[3] c95755e4bc
[4] 62d5761ddb
* resolve#1392
* pull in the fix for shirou/gopsutil/#249 which updates
the Linux driver for `cpu` to set `cpu.Mhz` to the maximum
clock-speed of the CPU, if that's available
