add flag to fail on first error, or to print the error inline when it occurs

[drewbanin]

It's presently tedious to debug a long-running dbt invocation. If a failure occurs, you need to wait until the invocation completes to see the error. This is prettier for most runs, but can be frustrating for long-running development runs.

Proposed flags:

• add a -x command to fail on first error
• add a --nocapture command to spit out errors as they occur?

[cmcarthur]

I like -x, --fail-on-error