CloudWatch Metrics Collector fails to publish metrics with small values

[ryanewel]

CloudWatch metrics can't accept metrics with magnitude < ~4.257959840008151e-109. Publishing metrics of this magnitude will cause the following error message:

ERROR [/cloudwatch_metrics_collector]: [AWSClient] HTTP response code: 400
Exception name: InvalidParameterValue
Error message: The value 0 for parameter MetricData.member.8.Value is invalid.

Steps to reproduce:

1. Launch the CloudWatch Metrics Collector with roslaunch cloudwatch_metrics_collector sample_application.launch
2. Publish small metrics with:
   rostopic pub -r 0.5 /metrics ros_monitoring_msgs/MetricList '{metrics: [{metric_name: 'too_small', value: 2.1289799200040754E-109, time_stamp:{secs: <time>, nsecs: 0}}]}'

Proposed Solution:
Add an option to round small values to 0 before publishing to Cloudwatch