Number of channels is hard-coded in stream.sh for node type = research

[scottveirs]

Noticed 2 channels in .mp3 file from Sunset Bay (concatenated .ts segments, transcoded), when there is only one hydrophone deployed and I'd set CHANNELS=1 in the .env file. Looked at current master branch in node/stream.sh and saw that $CHANNELS is used within the ffmpeg call for node type hls-only but for node type research it is still hardcoded as -ac 2 ...

## Streaming HLS with FLAC archive 
	nice -n -10 ffmpeg -f jack -i ffjack \
       -f segment -segment_time "00:00:$FLAC_DURATION.00" -strftime 1 "/tmp/$NODE_NAME/flac/%Y-%m-%d_%H-%M-%S_$NODE_NAME-$SAMPLE_RATE-$CHANNELS.flac" \
       -f segment -segment_list "/tmp/$NODE_NAME/hls/$timestamp/live.m3u8" -segment_list_flags +live -segment_time $SEGMENT_DURATION -segment_format \
       mpegts -ar $STREAM_RATE -ac 2 -acodec aac "/tmp/$NODE_NAME/hls/$timestamp/live%03d.ts

the -ac 2 part should be replaced with -ac $CHANNELS and then some tests should be run to ensure that the streamed audio sounds ok (single channel .ts segments play as stereo) and that we're being efficient with S3 storage (i.e. FLAC file has only one channel).