Don't run volumes/disks checking in case
if node was provisioned

* add checking if node was provisioned
* make checking methods as protected
  instead of private, because they
  shouldn't be private from design point
  of view, it simplify unit testing

Closes-bug: #1262973
Change-Id: I036c16138c48054579eb1d8388d048ac7331c041
Merge "Don't run volumes/disks checking in case if node was provisioned"