Always display path of test files

[taiki-e]

Currently, the way file names are displayed is different when both pass and compile-fail are present, and when only one is present. This patch unifies the way file names are displayed.

This makes the message displayed a bit redundant, but I think it is preferable to the current one for the following reasons:

• Easy-to-read messages in cases where users want to group tests, like Allow printing full test paths upon cargo test #94.
• Consistency with the path display format in stderr files, introduced in 508b39f. ($DIR/file.rs -> path/file.rs)

Closes #94