Refactor test boot methods

- Common code consolidated into CDROTestRunner and CDROTestIPhoneRunner
- CDROTestIPhoneRunner subclasses CDROTestRunner
Update podspec to not exclude CDROTestRunner on iOS
Don't try to call UIApplicationMain to kick off tests if no UIApplication instance is available
Hijack both OCUnit and XCTest for OS X test bundles
Merge pull request #241 from pivotal-brian-croom/refactor-boot-methods2

Refactored boot methods.