Better error message - test reporter fails on paths without prefix

[SimonBaeumer]

Hey codeclimate Team,
first of all thank you for your free open source offering, it already helped me a lot!

I run into this issue while migrating from travis to circleci, which was easily resolved by providing --prefix github.com/commander/commander-cli:

$ test-reporter after-build -t gocov
ERRO[0000] failed to read file github.com/commander-cli/commander/cmd/commander/commander.go
open commander.go: no such file or directory
Error: open commander.go: no such file or directory

It was relatively hard to debug I would like to extend the error message with a suggestion to use the --prefix option.

Example:

open commander.go: no such file or directory
Error: open commander.go: no such file or directory
Consider using --prefix to trim file paths.

If it is a go specific problem the error message could also suggest the prefix input.

Let me know what you think. I could provide you this small PR if it is appreciated.

[TihomirIvanov]

Thank you for reporting this. I had exctly the same isssue and adding --prefix fixed it