bugfix: do not generate dep conditions when no dependency
bugfix: do not generate dep conditions when no dependency

We only consider test dependencies some of the time. Some packages are
*only* test dependencies. Spack's algorithm was previously generating
dependency conditions that could hold, *even* if there was no potential
dependency type.

- [x] change asp.py so that this can't happen -- we now only generate
      dependency types for possible dependencies.

LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack