Existing targets running based on rbe need to specify:

"gclient_variables": {
                "use_rbe": true
            },

and

"gn": [
                "--rbe",
                "--no-goma"
          ]

Tons of duplication are in each subbuild's configs. We can have recipes to auto append gn configs based on the use_rbe gclient variable. The assumption is: "use_rbe": true is quivalent to "--rbe" && "--no-goma"