Previously, xcodeMajorVersion and xcodeMinorVersion returned null unless
xcodeVersionSatisfactory had been called first. We now compute them on
demand, and cache the resultant values.
Moves all remaining calls to tools that are part of the libimobiledevice
suite of tools to the IMobileDevice class. This allows for better
tracking of this dependency, and easier mocking in tests.
* Before tests
* Add the part to trust the cert on the device
* flip the error checks since some are more specific and are more actionable
* add tests
* review
