Add CPU affinity and process priority control

[ehpor]

Pin certain services on specific cores and set the priority of their process. Both are modifiable by the config.

An example config (should be in testbed.yml):

cpu_affinity:
  HICATDEUX:
    zernike_control_loop: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
    boston_dm: [16, 17, 18, 19]
    default: [20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31]
process_priority:
  HICATDEUX:
    boston_dm: high
    zernike_control_loop: high

Fixes #48

[raphaelpclt]

Looks good