macaroons: ensure all bytes read from db are copied before returning
macaroons: ensure all bytes read from db are copied before returning

This commit is a precautionary commit put in place in order to ensure
that the logic of macaroon retrieval doesn’t run into a bug triggered
by returning a reference into bolt’s active memory map. This can arise
if one returns a pointer directly read from the database. We seek to
avoid this by instead ensuring all byte slices are fully copied before
returning.

ddustin/lnd,LightningNetwork/lnd,ddustin/lnd,LightningNetwork/lnd,aakselrod/lnd,aakselrod/lnd