specs against physical devices

## motivation

This PR got a bit out of hand because Xcode 6 beta 5 was released while I was working on it.

The original intent was to provide specs testing against devices.  As you might imagine, such tests are difficult to manage.  The difficulty was compounded by the fact that b5 breaks launching against devices [1] and introduced some subtle changes to way instruments reports things like templates and devices.

There is support for testing against devices, but these specs are not run by default.  See the **test** section for details.

I tried to improved the readability of the specs especially around regression testing against Xcode versions.

## tests

#### sims

```
# testing against Xcode 5.0, 5.0.1, 5.0.2, 5.1, 5.1.1, 6b4
# some tests are skipped for Xcode < 5.1 - gotta draw the line somewhere.
$ be rake spec
Finished in 2 minutes 4.8 seconds (files took 1.85 seconds to load)
131 examples, 0 failures
```

#### devices

Requires:

* ideviceinstaller is in your PATH
* You might need to resign spec/chou-cal.ipa (iOS 8/Xcode 6 are funny about code signing).

Expect Xcode 6b5 to fail and Xcode 6b4 to pass.

```
# tests against all connected devices
# only tests Xcode >= 5.1 - gotta draw the line somewhere
$ be rspec spec/run_device_spec.rb

```

## links

- [1] [UIAutomation CLI Fails](https://gist.github.com/jmoody/27a3378d8d641b7f9012#4-uiautomation-cli-fails)