Mock xcrun calls

[imurchie]

Three unit tests still actually made system calls to xcrun. Mock those.

@mykola-mokhnach Can you run the existing utils unit tests (npm run build && npx mocha -R spec build/test/unit/utils-specs.js) before trying this patch? If the same three TypeError errors come up, then that kind of confirms this is the place. Then with this patch those should be gone.

That would also confirm that the problem is somewhere in the system call, which sucks. I would suggest at that point going into teen_process and trying to exec the xcrun --sdk iphonesimulator --show-sdk-version and see where the error comes up.

I wish I could reproduce this so I could investigate. :(

[mykola-mokhnach]

npm run build && npx mocha -R spec build/test/unit/utils-specs.js

> appium-ios-driver@4.2.2 build /Users/elf/code/appium-ios-driver
> gulp transpile

[07:46:20] Using gulpfile ~/code/appium-ios-driver/gulpfile.js
[07:46:20] Starting 'transpile'...
[07:46:24] Finished 'transpile' after 4.01 s


  prepareIosOpts
    ✓ should use instruments without delay by default
    ✓ should use instruments without delay if explicitly not using native instruments
    ✓ should not use instruments without delay if using native intruments


  3 passing (22ms)

These are fine

[mykola-mokhnach]

Also I cannot imagine how undefined could be returned from teen_process, because it can ONLY resolve to a dictionary: https://github.com/appium/node-teen_process/blob/30ab25a454b19507a3050fa9dd6613d6edb6470b/lib/exec.js#L92

[mykola-mokhnach]

this is an async call, btw