Fix #355, Adds fsw/src to app target

[chillfig]

Checklist (Please check before submitting)

• [x] I reviewed the Contributing Guide.
• [x] I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution -Fixes #355

Testing performed make install

Expected behavior changes Successful cert_testbed build

System(s) tested on

• Ubuntu 20.04

Additional context N/A

Third party code N/A

Contributor Info - All information REQUIRED for consideration of pull request Justin Figueroa, Vantage Systems

[chillfig]

cert_testbed required changes elsewhere to resolve build errors. The option to include fsw/src to app target from the open-source code is not preferred.