fix: reporter config option

[fson]

This PR backports the fix from #370 to the 1.x branch. I cherry picked 809aef9 to 1.x.

Summary:

The loadConfig function in metro-config reads the reporter option
from the second argument (defaultConfigOverrides) instead of the
first argument (argv), so we need to pass it in that object to
make the customLogReporterPath CLI option work.

Test Plan:

1. Created a file reporter.js with the following contents:

class JsonReporter {
  update(event) {
    console.log(JSON.stringify(event));
  }
}

module.exports = JsonReporter;

2. Ran this command and inspected that the output was JSON:

node ~/Projects/react-native-cli/packages/cli/build/index.js start --customLogReporterPath ~/Projects/react-native-cli/reporter.js

[thymikee]

Thanks! Released 1.9.3 with this patch