Allow excluded bogus runs from being plotted in the perf history

[qinsoon]

We track performance for all of our commits (e.g. https://www.mmtk.io/ci-perf-result/master/openjdk_semispace_history.html). However, we may have some bogus runs that were recorded and plotted in the graph. This PR along with the change in ci-perf-kit (https://github.com/mmtk/ci-perf-kit/releases/tag/0.6.7) allows us to manually exclude certain runs from being plotted in the graph.

https://github.com/mmtk/ci-perf-kit/releases/tag/0.6.7 also fixes an issue that runs with no valid results will no longer be plotted as 0 in the graph. Instead, the graph will show a blank result for the run.