Print error context when a benchmark fails to run

Before:

```
collector error: Failed to benchmark 'stm32f4', recorded: failed to obtain pkgid in '"/tmp/.tmpLF63db"'
```

After:
```
collector error: Failed to benchmark 'stm32f4', recorded: failed to obtain pkgid in '"/tmp/.tmpAmktlm"': expected success, got exit code: 101

stderr=error: a Cargo.lock must exist for this command

 stdout=
```

Author: jyn514

collector/src/main.rs

@@ -255,7 +255,7 @@ fn bench(
             benchmark.measure(&mut processor, build_kinds, run_kinds, compiler, iterations);
         if let Err(s) = result {
             eprintln!(
-                "collector error: Failed to benchmark '{}', recorded: {}",
+                "collector error: Failed to benchmark '{}', recorded: {:#}",
                 benchmark.name, s
             );
             errors.incr();