feat(signalfx-reporter): add additional debug logging

[fieldju]

Adding some new debug statements for the SignalFx reporter to enable easier prod support.

EX: from UAT

AP77JGH6A84FA3:node-measured jfiel2$ node packages/measured-signalfx-reporter/test/user-acceptance-test/index.js 
2019-08-28T22:51:45.646Z:  SignalFx Metrics Reporter Created with the following default default reporting interval: 10, default dimensions: {
  "app": "measured-signalfx-reporter",
  "app_version": "1.50.0",
  "env": "test"
}
2019-08-28T22:51:45.649Z:  _createIntervalCallback() called with intervalInSeconds: 30
Example app listening on port 8080!
2019-08-28T22:51:45.665Z:  _reportMetricsWithInterval() called with intervalInSeconds: 30
2019-08-28T22:51:45.665Z:  _reportMetrics() called
2019-08-28T22:51:45.666Z:  Sending data to Signal Fx. Request: {"gauges":[{"metric":"node.os.loadavg.1m","value":2.26171875,"dimensions":{"app":"measured-signalfx-reporter","app_version":"1.50.0","env":"test"}},{"metric":"node.os.loadavg.5m","value":2.443359375,"dimensions":{"app":"measured-signalfx-reporter","app_version":"1.50.0","env":"test"}},{"metric":"node.os.loadavg.15m","value":2.330078125,"dimensions":{"app":"measured-signalfx-reporter","app_version":"1.50.0","env":"test"}},{"metric":"node.os.freemem","value":7081623552,"dimensions":{"app":"measured-signalfx-reporter","app_version":"1.50.0","env":"test"}},{"metric":"node.os.totalmem","value":34359738368,"dimensions":{"app":"measured-signalfx-reporter","app_version":"1.50.0","env":"test"}},{"metric":"node.os.uptime","value":109451,"dimensions":{"app":"measured-signalfx-reporter","app_version":"1.50.0","env":"test"}},{"metric":"node.os.cpu.all-cores-avg","value":31,"dimensions":{"app":"measured-signalfx-reporter","app_version":"1.50.0","env":"test"}},{"metric":"node.process.memory-usage.rss","value":61145088,"dimensions":{"app":"measured-signalfx-reporter","app_version":"1.50.0","env":"test"}},{"metric":"node.process.memory-usage.heap-total","value":35401728,"dimensions":{"app":"measured-signalfx-reporter","app_version":"1.50.0","env":"test"}},{"metric":"node.process.memory-usage.heap-used","value":21408856,"dimensions":{"app":"measured-signalfx-reporter","app_version":"1.50.0","env":"test"}},{"metric":"node.process.memory-usage.external","value":550020,"dimensions":{"app":"measured-signalfx-reporter","app_version":"1.50.0","env":"test"}},{"metric":"node.process.uptime","value":0,"dimensions":{"app":"measured-signalfx-reporter","app_version":"1.50.0","env":"test"}}]}
^CSIG INT, exiting

[fieldju]

@rdong333

[coveralls]

Pull Request Test Coverage Report for Build 419

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 89.189%

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Totals
Change from base Build 415:	0.04%
Covered Lines:	772
Relevant Lines:	848

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💛 - Coveralls