profile: testing scaffold

A simple scaffold for testing various profile options and observing the output.

Updates #7 
Would everything not be easier as:
```go
type checkFn func(t *testing.T, stdout, stderr []byte, err error)
```
In this way everything would become more readable, and you could drop the variadic-to-slice function.

Or do you feel the same way [as here](https://github.com/pkg/profile/pull/4#discussion-diff-19383042R19) about it?