Update DCM scheduler

[hunhoffe]

This PR:

• Cleans up RPC library (remove overly verbose code in preparation to rework portions of the library)
• Reduces RPC header size (required updating nrk-dcm-scheduler)
• Adds support for different scheduler backends in integration tests (required updating nrk-dcm-scheduler)

This version of nrk-dcm-scheduler supports the following backends:

• R (random scheduler)
• RR (round robin scheduler)
• LF (local-fill scheduler, previously called sticky scheduler)
• DCMcap (DCM with only capacity policy - this performs poorly due to being under-constrained)
• DCMloc (DCM with cap + locality policy - includes upgrade locality policy from previous version of DCM.

The dcm runner in the nrk integration tests is able to take an argument to specify the scheduler backend.