SignOut after every auth user test
SignOut after every auth user test

SignOut in a correct manner instead of setting null pointers.
If we do not sign out, there could be information in the persistent cache
that can prevent a subsequent sign in from happening and cause the tests to
run incorrectly (saw errors when running on github mac runners)

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