use DTiPhoneSimulatorRemoteClient instead of iPhoneSimulatorRemoteClient

This is working towards the fix for `iPhoneSimulatorRemoteClient` not
working on iOS 7.1 / Xcode 5.1 DP.

It's going to let us pass a lot more info to the iPhone Simulator,
including device name and architecture.
Make xctool compatible with Xcode 5.1

- Respect `-destination` option when running iOS tests.
- Support running test without `-destination` option specified.
- Validate `-destination` option value before running any actions:
1) check whether device with provided `name` exists,
2) check whether iOS sdk with provided `os` version exists,
3) check whether provided device supports provided sdk (only if both os version and device name are provided).
- Add `-destination-timeout` option support.
- Don't update valid `-sdk` flags

Details:
1) Validation of `-destination` option is done using `SimulatorHost.framework`. This frameworks gives us reference to all available sdks and devices.
2) Moved destination option parsing into `XCToolUtil`.
Merge pull request #336 from facebook/nekto/add_xcode51_support

Make xctool compatible with Xcode 5.1