Two validation functions to be used by the barclamp-ceph repo.

* validate_count_as_odd_for_role
  As the name describes we want to check that we have an odd number
  of nodes used in a role.

* validate_count_as_even_for_role
  Same as the above but checking for even number of nodes in a role.

Signed-off-by: JuanJose 'JJ' Galvez <jj.galvez@inktank.com>