syncbase: Get the login to work by adding a testLogin option

This change adds a testLogin option to the set of option we can pass
to Init in the high-level Syncbase API. When set to true the testLogin
will cause the call to login() to generate a 'root:o:app:user'
blessing which will set the app name to 'app' and the user name to
'user'. This also fixes the tests from internal/BlessingsTest.

Note: the author of the Swift code is Aaron Zinman <aaron@azinman.com>.

MultiPart: 2/3
Change-Id: Idd001a0a87dbd2e49453a28a1c65d3dde246e4ee
16 files changed