[disks] Add key allocate_size to volumes_role_mapping.
This key can have value
* min - allocate min size
* all - means allocate all free space,
  if node has serveral volumes with such
  key, allocator allocate equal size for
  each volume
[disks] change order of fields in volume-role mapping
[disks] Fix allocation logic, use key allocate_size from role-volume mapping
* firstly allocates volume which required min size allocation
* then allocate other volumes with equal size
[disks] add more verbose comment
[disks] fix terms s|vg|volume|
[disks] fix tests for minimal installation
[disks] fix equal volume allocation
[disks] fix validator test, skip cinder becuase it does not have logical volumes
[disks] remove unused parameter for _allocate_all_free_space_for_volume
[disks] fix comment
[disks] add tests for multirole
[fixtures] fix volume-role mapping for redhat and ubuntu
Merge pull request #1614 from Mirantis/multiroles-disk-allocator

Multiroles disk allocator [PRD-1603]