fix(flux): Call storage API to correctly map group mode
fix(flux): Call storage API to correctly map group mode

This fix ensures group(mode:"by") is correctly pushed down to the
storage layer.

influxdata/influxdb,mark-rushakoff/influxdb,li-ang/influxdb,influxdb/influxdb,influxdb/influxdb,influxdb/influxdb,nooproblem/influxdb,influxdb/influxdb,mark-rushakoff/influxdb,nooproblem/influxdb,mark-rushakoff/influxdb,nooproblem/influxdb,mark-rushakoff/influxdb,mark-rushakoff/influxdb,influxdb/influxdb,nooproblem/influxdb,nooproblem/influxdb,influxdata/influxdb,influxdb/influxdb,li-ang/influxdb,mark-rushakoff/influxdb