Disk: Non-linear contraints

Disk: Non-linear contraints

Users can now define a callback to set the capacity of the resource
during the system solve. The callback receives the current capacity and
number of activities/flows currently sharing the resource.

The capacity is defined once at the beginning of the system solve.

- Disk:
  - Add API to set sharing_policy by type: read/write/read-write
  - Example: io-degradation: simulates the degradation in read/write
operation on disks.