increase flexibility of determining influx database params

brian_polling_manager/influx.py

brian_polling_manager/interface_stats/cli.py

brian_polling_manager/interface_stats/services.py

brian_polling_manager/interfaces.py

brian_polling_manager/sensu.py

test/interface_stats/test_interface_stats.py

test/interface_stats/test_interface_stats_e2e.py