Unhardcode netapp and scheduler options

this patch makes it possible to set custom filter_function and
goodness_function for the NetApp backend in Cinder.

In order for those to have any effect, the scheduler_default_filters
and scheduler_default_weighers optios are also unhardcoded so
appropriate filters and weighers can be enabled in their values.

Change-Id: I26dd040fa7cffa2d00440b8688bd04b15b64a0f4
Closes-Issue: PROD-33656
9 files changed