Fixes for running generation with a facet override and other generation improvements.

- Facet can only be applied once project artifacts are discovered, otherwise
facet thinks no artifacts are valid.  In future we should update artifact
session code to update the applied facet lookup maps each time an artifact
is added to the session to account for this.
- In plugin run report, give resolved generator version instead of the plugins
configured mininmum version.
- In case of error running generation, fail generation right away, to make it
easier to identify the source of failure, instead of needing to scroll back
through logs to try to find where an error was printed.  Especially helpful
when running multi-threaded project generation.
- In case plugin cannot be loaded, possibly because minimum required version not
present, fail generation right away instead of  silently skipping it.

Change-Id: Id5983d1b089e9dd68aa515302f2805284d0b543d
8 files changed