I watched VII for the third time last night and came to the conclusion that Rey isnt a Skywalker but...
I then thought about the slave thought and this is what I think.
Luke is retracted after the loss of everything. He had a acquaintance (who's force sensitive and a daughter whom is in his academy) and he doesnt know what has happened to them.
Rey in the panic at the rise of the first order is taken by her mother to the outer rim where she is deemed safe with her lineage unknown by Jakku residents. Luke since the oblitoration of his academy has found the Jedi temple so as close to the force as possible therefore being able to feel awakening (disturbance in the force) of his daughter (as her whereabouts to him are unknown) this happens with the bb8, rebellion encounter and subsequent duel with kylo, he then triggers R2 to reveal his location to the rebels in the hope she will come. As we know she does and the realization and torture in his face says it all. He still has a daughter and that she is stood in front of him with HIS saber.
Now whos is the mother? I'm going with Capt Phasma. The obedient servant of the first order is Reys Mother. In the attack on the Jedi Academy, Phasma helps Kylo Ren destroy the temple and destroying with it Lukes trust but its a risk she feels she HAS to take to protect their daughter. Years prior to the massacre she has taken Rey from Luke and takes her to the Outer Rim to be safe and joined the first order to keep an ear to the ground and Luke does not know the whereabouts if her or Rey.
The way Phasma is Lenient with Finn and doesnt take part in the killing and then lets the sheilds be lowered without too much resistance as to not risk her life. Is all too nice for the FEARED Capt Phasma. I also think she have something to do with turning the Storm troopers clones back to the 'republic' as its frequently stated they are traitors at a wim by Kylo.
I dont think it will be revealed in VIII but we will be left with no doubt.