Add process package

[nirs]

Current code contains multiple implementations for managing a process
using pids, with various issues:

• Some are unsafe, terminating a process by pid without validating that
  the pid belongs to the right process. Some use unclear
• Using unclear terms like checkPid() (what does it mean?)
• Some are missing tests

Let's clean up the mess by introducing a process package. The package
provides:

• process.WritePidfile(): write a pid to file
• process.ReadPidfile(): read pid from file
• process.Exists(): tells if process matching pid and name exists
• process.Terminate() terminates a process matching pid and name
• process.Kil() kill a process matching pid and name

The library is tested on linux, darwin, and windows. On windows we don't
have a standard way to terminate a process gracefully, so
process.Terminate() is the same as process.Kill().

I want to use this package in vfkit and the new vment package, and later
we can use it for qemu, hyperkit, and other code using managing
processes with pids.

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @nirs. Thanks for your PR.

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[nirs]

@medyagh this should be used in #20506 and #20501.

[minikube-bot]

Can one of the admins verify this patch?

[medyagh]

thank you @nirs I would suggest making use of this package in this same PR, generaly we dont merge code which is not used yet, it would be better to be used in the same PR and be tested and then we dont have to do a difficult revert if later we find out it is not what we wanted

[nirs]

thank you @nirs I would suggest making use of this package in this same PR, generaly we dont merge code which is not used yet, it would be better to be used in the same PR and be tested and then we dont have to do a difficult revert if later we find out it is not what we wanted

This code is already used in #20506, so I'm closing this one.