Ensure there is a newline after the nodepool keys

Infra are now adding 2 jenkins keys to the nodepool instances
I6579560aaff782b78ba06dfc134e5ec6f9848aff
But the second key is no longer followed by a newline so we need to add
one in order to ensure two public keys aren't concatenated.

Change-Id: Ibfc3d6f5eb5b3327834b5b1ae58be5327c914ef7