Reset locked_by when unlocking a Node

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Tweak logic of setting Node.up

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Don't recycle locks if description isn't passed

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>