Add test coverage of default scopes

[chlowell]

• MSAL needs to add "openid profile offline_access" to request in order for caching to work. These should just be ignored when it comes to caching.

openid + profile tells AAD to issue an IdToken
offline_access tells AAD to issue a refresh token.

Originally posted by @bgavrilMS in #327 (comment)

I observe this behavior empirically, and the relevant code looks correct, but I don't find any unit tests covering it. My first thought is, call the From* methods of accesstokens.Client, verify the scopes with a fake urlFormCaller. It would be nice to test this at the application level instead, say with a fake HTTP client, but faking everything else necessary to make that work would be more complex.