Update build to work with interface libraries

[jphickey]

Is your feature request related to a problem? Please describe.
As part of nasa/cFE#972 and PR nasa/cFE#1203 the directory structure of CFE is changing. The sample_app build script was directly referencing certain CFE paths that will need an update after this merge.

Describe the solution you'd like
Utilize additional wrapper functions and interface libraries to facilitate the path change and avoid issues in the future.

Additional context
See also nasa/cFE#1207 to add wrapper functions that will help with the unit test aspect

Requester Info
Joseph Hickey, Vantage Systems, Inc.