MultiAppCopyTransfer does incorrect sanity checks on variable names

[permcody]

Bug Description

Variable checks on MultiAppCopyTransfer appear to be incorrect. See discussion here:
https://groups.google.com/d/msgid/moose-users/CACL%2BgcNW87P5QzVPD%3DQAuxYR945cao6enJCjmi24boPY72rWTQ%40mail.gmail.com?utm_medium=email&utm_source=footer

Steps to Reproduce

master.i

[Problem]
  solve = false
[]

[Mesh]
  type = GeneratedMesh
  dim = 2
[]

[MultiApps]
  [./sub]
    type = TransientMultiApp
    input_files = sub.i
  [../]
[]

[Transfers]
  [./from_sub]
    type = MultiAppCopyTransfer
    direction = from_multiapp
    multi_app = sub
    source_variable = aux
    variable = x
  [../]
[]

[AuxVariables]
  [./x]
  [../]
[]

[Executioner]
  type = Transient
[]

sub.i

[Problem]
  type = FEProblem
  solve = false
[]

[Mesh]
  type = GeneratedMesh
  dim = 2
[]

[AuxVariables]
  [./aux]
  [../]
[]

[Executioner]
  type = Transient
[]

Impact

Minor: Affects only a single Transfer