Log the origin of required resources when initializing

[natekupp]

Saw this in the logs as I'm trying to update "spark" to "pyspark":

dagster_examples_tests/airline_demo_tests/test_types.py 2020-03-22 13:01:48 - dagster - DEBUG - spark_df_test_pipeline - eafd4196-4fad-42bc-bbcf-d264f7d923b0 - ENGINE_EVENT - Starting initialization of resources [pyspark, spark].

It's super helpful to see what resources are being initialized (this was my clue I had missed something) - but would be even better to log where the resources are being required from. In this case I was bit by #1983

[natekupp]

Would be nice to have a summary like:

Starting initialization of resources:
pyspark - required by solid instances [foo, bar]
spark - required by ...
...