Previously initializing the DependencyProcessor will result in file IO.
In a fully-hermetic environment where all dependencies are local, this IO is redundant and may require the build system (e.g. Bazel) to do extra setup to ensure there is a local writable directory specified for these directories. This change will instead cause the dependency processor to bail early and skip downloading dependencies if all are local anyway.
Prior to this change kicking off a clean build with local dependencies would result in:
```
rm -rf ~/.konan/cache; fswatch -ax ~/.konan
~/.konan/cache Created IsDir
~/.konan/cache/.lock Created IsFile
```
After the change no FS operations are performed.
Martin Petrov
416d12bce8