Coverage report includes test LOC

Right now we're using a tool called cargo-travis that provides a convenience wrapper to kcov for generating and publishing coverage reports to Coveralls. It does not expose the --exclude-pattern or --exclude-file options that would allow us to keep lines of test code out of the report.

It would be nice to manage building/caching/running kcov without the cargo-travis wrapper in order to get a more accurate representation of our current test coverage.