fix for null output for tests defined in ephemeral dir [development]

[drewbanin]

Previously, schema.yml files defined in models configured with materialized: ephemeral were effectively ignored by the dbt runner. dbt did not distinguish between ephemeral models and tests.
While it's a little strange that tests even have a materialized config, they are "resources" and adhere to the same contract as models. This branch fixes #501

Before:

Found 3 models, 1 tests, 0 archives, 0 analyses, 30 macros, 0 operations

14:32:34 | Concurrency: 1 threads (target='dev')
14:32:34 |

Completed successfully

Done. PASS=2 ERROR=0 SKIP=0 TOTAL=2

After:

Found 3 models, 1 tests, 0 archives, 0 analyses, 30 macros, 0 operations

14:32:34 | Concurrency: 1 threads (target='dev')
14:32:34 |
14:32:34 | 1 of 1 START test unique_events_generate_series...................... [RUN]
14:32:37 | 1 of 1 PASS unique_events_generate_series............................ [PASS in 3.18s]

Completed successfully

Done. PASS=1 ERROR=0 SKIP=0 TOTAL=1

[cmcarthur]

@drewbanin looks good to me