nanny: make policy application mechanism aware of children dependency

nanny: cleanup of apply policy functions:
    - ni_factory_device_apply_policy()
      Do not generate config. Config must be already
      generated (fail otherwise)
    - ni_managed_device_apply_policy()
      Generate config from policy only when not already
      done.

fsm: cleanup of ni_fsm_policy_applicable()
    - move common checks to the caller
    - removed unnecessary debug messages
    - cleanup comments

fsm: check only given worker's name on <device>
fsm: change ni_fsm_exists_applicable_policy param

ifup: <match> recursive <child> generation