Integration tests

[sethp]

In tests/config.rs there's something like 6 tests named with a variation of hello_world2. They're testing something useful, but it's not clear what from the way the code is currently structured. We should clean these up:

• hello_world: produces a listing of what ssh -G output looks like to the terminal. So far I've used this mostly as a point of reference when other tests fail. Is there another way to give the output we expected to see context when one of the other tests fail?
• hello_world2: produces the default ssh config, but doesn't check it against anything yet
• hello_world3, hello_world_4, hello_world5: all of these have some variation on the theme of "what will the ssh binary parse this weird config option to?" (for many of these, there's a matching behavior in ssh2-config, but we're not demonstrating that explicitly with any tests)

In addition, quoted_token_config and multi_line_quoted_token_fails both more or less fall into that last bucket, though they're a little clearer about what they're testing and actually asserting something meaningful.

It seems like there's room to pull out a test macro that's something like:

given this ssh config
when openssh parses it 
 and ssh2-config parses it
then they produce the same result