xcode6 sim prefs plist changed location

Replaces https://github.com/calabash/calabash-ios-server/pull/56

The are semantically identical, but PR #56 would need a rebase + force push and a code-level fix.

#### notes

@krukow 

I noticed that the plist does not exist _until something is written to it_.  I am not sure if this will have any consequences RE: interacting with UIA.

I added code comments that describe the behavior.