Consistently ensure dog_stats_api tags are formatted correctly
Added handling in gitlog for missing import logs

Fixes a template error that occurs when viewing a course's detailed
git import log. The problem happens for courses imported using methods
other than the `git_add_course` command.
Merge pull request #5431 from open-craft/datadog-wrapper

Consistently wrap the DataDog API to prevent logged errors & missing stats data
Merge pull request #5423 from mitocw/bdero/fix-gitlog-focused-error

Added handling in gitlog template for missing import logs
pylint cleanup.
Merge pull request #5560 from edx/benp/improve-pylint-violations

pylint cleanup.
Fail paver tasks when a given change's quality and coverage dip too low.

Also upgrades diff-cover in order to take advantage of this funcitonality.
Print diff-cover output in case of failure.
Add description to percentage flag being used.
Use specific hash instead of tag.
Increase quality expectations, lint improvement.