Allow customization of included classes via hieradata

Allow customization of included classes via hieradata

Allows inclusion of additional arbitrary puppet classes by the
manifests if defined in the *_classes hieradata.

Example: to specify the Nova RAM allocation ratio there is a
param in nova::scheduler::filter but we do not include it
by default; if needed one can use:

  nova::scheduler::filter::ram_allocation_ratio: 1.8
  controller_classes:
    - nova::scheduler::filter

Change-Id: I61d64d2498bed5c49376dee917d106598392db51