[PATCH v1] dts: fix pass rate edge case in results json

[Dean Marx]

Also, I noticed after submitting this first version that suites where
some cases are skipped and the rest pass have a 100% pass rate in the
results report. Should this also mean that suites where every case is
skipped have a 100% pass rate? Right now this reports a 0% when the
entire suite is skipped, if anyone thinks this should be changed let
me know.