The build should be modularized

[lwrage]

Currently we build everything on any change.
The build should build parts of osate, instead, and then assemble the product from the parts.

child of #920

[lwrage]

The nightly build creates p2 repos for smaccm and osate2-ocarina. These are used by the pull request builder.

[lwrage]

Need build configurations that check for changes in certain sub-directories of the osate2 repo.