Benchmark gardening

Summary: The php-octane benchmarks should behave better when included
multiple times in the same VM invocation.

Modified the normalization factor for DeltaBlue because we weren't
getting enough precision after normalization + rounding.

Duplicated run.php to harness-run.php which includes only a single
(non-existent) include.php file. This layer of indirection will allow
tools to more easily control which benchmarks are run in a single VM
invocation by dynamically generating include.php with the desired files.

Also added a suites.json file to document the benchmarks that exist in a
way that's amenable to scripting.

Reviewed By: @jdelong

Differential Revision: D1600694