Xcode 6 support for specifying the os version of the simulator

When pull request 91 (Added initial Xcode6 beta (6A215l) support) was merged in, it did not allow you to choose between conflicting device identifiers.
For example you could have:
* com.apple.CoreSimulator.SimDeviceType.iPhone-4s
* A bunch of other identifiers
* com.apple.CoreSimulator.SimDeviceType.iPhone-4s

This will happen if you have your iOS 8 sdk, and any old iOS simulators (iOS 7.0.3 or 7.1) installed.

In order to differentiate between the simulators, it will print out

* com.apple.CoreSimulator.SimDeviceType.iPhone-4s, 7.0.3
* com.apple.CoreSimulator.SimDeviceType.iPhone-4s, 8.0

Then you use as you would before:
```
./ios-sim --devicetypeid "com.apple.CoreSimulator.SimDeviceType.iPhone-4s, 8.0"
```

The old way which does not include the iOS version in the string will still work by looping through the devices and selecting the first one with a matching identifier.