Bug fixes and Greengrass sample enhancements

Enhancements

• Remove websocket flag in the agent connection setup
• Read configuration from environment variables in the Greengrass lambda
• Add unit tests for the Collector class
• Add optional "Thing Name" command line parameter in addition to Client Id
• Add ability to provide command line flags in a file, using @file syntax

Bug Fixes

• Network stats parameters were being passed out of order by the collector
• Delta stats were not calculated correctly