Guard Process.kill pid 1 spec in case user owns it

In some environments, the user running the spec might own pid `1` (even without being root).  It's also possible this spec could be run from _as_ pid `1`.  This is the case with Docker, in which the command you pass to `docker run` is run as pid 1.

```
jemc@localhost~/1/docker> sudo docker run -t -i rubinius ps
  PID TTY          TIME CMD
    1 ?        00:00:00 ps
```

In this situation, MRI will allow killing of pid 1 without exception (and so will `kill -9 1`).

The spec needs to guard this test and skip it when the current user owns pid 1.
@jemc the issues that make this spec hard are described in this comment https://github.com/rubyspec/rubyspec/pull/231#issuecomment-68009548.

As you say, it's not clear that what Ruby needs to assert is whether it can kill a process that can't be killed. There's also an argument that RubySpec should not spec any exceptions (ie code that does not successfully run), but because so much Ruby code rescues exceptions to do something else, I could see a bug that results from not raising a Errno::EPERM here. And if we don't have a spec for it, we don't know the behavior works.

I'm uncertain what is the best approach.