When a jvm doc tool (e.g. scaladoc) fails in combined mode, throw an exception.  Log runs of jvmdoc.  Eliminate unnecessary dict lookup.

Testing Done:
Ran tests.

Reviewed at https://rbcommons.com/s/twitter/r/1116/
Sync of https://github.com/pantsbuild/pants/commit/deb2f3180a4446080087d589b24d6a66b60ed033