Make sure that iterated elements are lists

For cases where single results are returned for `codeCoverage`,
`codeCoverageWarnings`, `successes`, `failures` make sure we convert to
a list before iterating. Example data in
https://github.com/joeferraro/MavensMate-SublimeText/issues/151
Merge pull request #31 from doublesharp/patch-unit_test-lists

Make sure that iterated elements are lists