Reworking user_bound for Exec actions.

Reworking user_bound for Exec actions.

Avoid using directly surf_action->set_bound to modify action's bound.

Actual bound is defined by CPU model, for cas01 is the min of:
- user's bound
- requested_core*speed*scale.

Explicitly deny the use of user_bound_ for ptask and cpuTI. We need
proper tests to verify their behavior.