lnwire: Trim zero-bytes from NodeAlias String representation
lnwire: Trim zero-bytes from NodeAlias String representation

This commit alters the NodeAlias String method to trim null-bytes from
the end of the alias. This is helpful for presentation in contexts such
as the GetInfo response.

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