Define okapi/tenant defaults

Many CLI operations require an Okapi and tenant value to be present. This includes building apps in isolation and running their tests.

Platforms contain tenant configurations that contain sample data. These values, "localhost:9130" and "diku", are also present in many documents and vagrant boxes. It would simplify things if the CLI were to offer these defaults without the user having to provide them on the command line or create a .stripesclirc when cloning an app repo.