Make `bin/phd debug` quieter by default
Summary:
By default, `bin/phd debug` activates `--trace`, which is incredibly verbose.
Instead, be moderately verbose by default, and only include tracing if `--trace` was passed to `bin/phd debug`.
See also D15422.
Test Plan:
- Ran `bin/phd debug task`, got moderate amount of most useful debug output.
- Ran `bin/phd debug task --trace`, got very verbose, detailed low-level debug output.
Reviewers: chad
Reviewed By: chad
Differential Revision: https://secure.phabricator.com/D15423