The "cpu" cgroup controller

Resolve the CPU cgroup controller for the current process

Throws an Exception if the CPU controller is not able to be found, or when running outside of a cgroup

A CPU quota is the amount of CPU time our process can use relative to the scheduler period

For example:

| cpu.cfs_quota_us | cpu.cfs_period_us | description |
| ---------------- | ----------------- | ----------- |
|           100000 |            100000 | (1)         |
|           200000 |            100000 | (2)         |
|            50000 |            100000 | (3)         |
|               -1 |            100000 | (4)         |

1. : we can use up to a single CPU core
2. : we can use up to two CPU cores
3. : the scheduler will give us a single CPU core for up to 50% of the time
4. : we can use all available CPU resources (there is no quota)

Get the CPU quota within the given cgroup CPU controller