Support multiple measurements for get_measurement_for_hosts()

[ajdavis]

The getHostMeasurements API supports multiple "m=" parameters. I know get_measurement_for_hosts lets you pass a Measurement class as the measurement argument, to indicate you want all the measurements that are members of the class. But I propose that measurement could also be a list of measurements for maximum flexibility, to expose all the possibilities of the API.

[mgmonteleone]

Good suggestion, and this could be done in the future. Perhaps someone can look at this and send a PR?