Add flags to disable JEDI tests as part of the GDASApp build process

[RussTreadon-NOAA]

The current GDASApp build compiles numerous JEDI tests and downloads test data. These tests are not always needed. Flags should be added to allow users to disable the building of tests and downloading of test data.

This issue is opened to track the changes needed to optionally turn off tests and the downloading of test data during the GDASApp build.