Discern between two possible error types

In trying to get to the bottom of why internal/command/uploadarchive/uploadarchive_te... (gitlab-shell#671) continues to sporadically occur, I traced the error that's sent into the errC chan to be one of two possibilities, but currently there's insufficient information to determine which call has caused the error. This MR wraps the two different errors with additional context so that if/when they are passed, we'll know more specifically which piece of logic caused it.

Related:

• Integration Tests for SSH Upload/ReceivePack (!178 - merged) (is where the logic was implemented)
• internal/command/uploadarchive/uploadarchive_te... (gitlab-shell#671)