[WIP] Convert KiwiTests to .xctest.

- Convert KiwiTests.octest to KiwiTests.xctest using Xcode 5 migration
  tool.
- All KiwiTests are now executed, including functional tests. Note that
  previously (e2290d7237) only 287 tests were executed; this commit
  returns that number to the same as on master, 304.
- Due to the fact that KiwiSpec does not provide file name or line
  numbers, individual assertions in functional tests are not displayed
  in Xcode 5 test navigator.
- .octest bundles are no longer executed.
[WIP] Add XCTest to podspec.