Initially there were pkg and private packages, however for all practical
purposes there's no significant difference between them. It's clearer to
have a single private package - and when we do get a specific
abstraction that needs to be reused, we can move it to storj.io/common
or storj.io/private.
Change-Id: Ibc2036e67f312f5d63cb4a97f5a92e38ae413aa5
Move a specific interface & types used for testing to be a private
subpackage with a name that clearly identifies it for testing purpose.
Change-Id: I646cf3b6f0a3b518a6f9a125998dc5a02df02db6
