After O process fails, B continues to report multiple renditions in the manifest, and serve stale transcoded content.

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## Bug Description

When an O/T process fails, the B continues to report transcoded renditions in the `.m3u8` manifest, and serves stale (cached, i.e. not live) transcoded content.

## Observed Behaviour

Steps to reproduce the behavior:

1. Download version 0.5.27 of Livepeer `wget https://github.com/livepeer/go-livepeer/releases/download/v0.5.27/livepeer-linux-amd64.tar.gz`
2. Unzip `tar -xzf livepeer-linux-amd64.tar.gz`
3. start O/T `./livepeer -orchestrator -transcoder -serviceAddr 127.0.0.1:8935 -v 99`
4. start B `./livepeer -broadcaster -httpAddr :8936 -cliAddr :7936 -rtmpAddr :1936 -orchAddr 127.0.0.1:8935 -transcodingOptions P720p30fps16x9,P576p30fps16x9,P360p30fps16x9,P240p30fps16x9,P144p30fps16x9 -v 99`
5. start `ffmpeg` to stream into B `ffmpeg -re -f lavfi -i testsrc=size=1920x1080:rate=30,format=yuv420p -f lavfi -i sine -c:v libx264 -b:v 10000k -x264-params keyint=60 -c:a aac -f flv rtmp://127.0.0.1:1936/test_source`
6. Run the following `curl http://localhost:8936/stream/test_source.m3u8`
7. Observe that multiple renditions being served by the B
8. Kill the O/T process (ctrl-C)
9. Run `curl http://localhost:8936/stream/test_source.m3u8` again
10. Observe that the B is still reporting multiple renditions being served
11. Run `ffplay http://localhost:8936/stream/test_source/source.m3u8`
12. Observe that the `source` rendition of live content is still being served (note the sequence number)
13. Run `ffplay http://localhost:8936/stream/test_source/P144p30fps16x9.m3u8`
14. Observe that a stale (not live) `144p` rendition is still served by the B (note the sequence number is lower than in step 12.)

## Expected Behavior

At step 10, I would expect the B to only be reporting availability of the `source` rendition.

At step 14, I would expect that no stale `144p` content is being served by the B.

## Environment

- Livepeer Version: `0.5.27`


## Additional Comments

None.

Reproduce the failure with the Livepeer 0.5.27 commands, focusing on the broadcaster's /stream/test_source.m3u8 endpoint after the O/T process is stopped. Compare the reported renditions and sequence numbers for source.m3u8 and P144p30fps16x9.m3u8; done means only source remains available and no stale transcoded content is served.

Written by the indexing model from the issue text.