Include space_guid in service provisioning requests

  This commit makes that piece of info visible to service gateways.

Change-Id: Iabf59ad5abfa642abaf06982b1f4519e01223f02
Set a proper message bus in AppStager specs

  This commits makes the tests use a proper mock message bus instead of
nil.

Change-Id: I0d2d8b0b26b9845a480ed318b4e4f4784ee27d91
Remove dead code

  current_user_guid became dead code after commit 699d116

Change-Id: I79bcf769d45b5491ac0c33774438ff669d89d529