Fix missing files when building integration test against prebuilt
Fix missing files when building integration test against prebuilt

The build script was previously using the SDK directory to look for the script to copy shared integration test files into the integration test directory.

This changes to use the root (repo) directory, so that it works both when building from source and when building from prebuilt.

firebase/firebase-cpp-sdk,firebase/firebase-cpp-sdk,firebase/firebase-cpp-sdk,firebase/firebase-cpp-sdk,firebase/firebase-cpp-sdk,firebase/firebase-cpp-sdk,firebase/firebase-cpp-sdk,firebase/firebase-cpp-sdk