[TSK] Correctly handle failure to connect to bootstrap server

[alistairking]

I'm not sure how to do this, but currently if one of the bootstrap servers are unavailable when starting up, libtimeseries will get stuck with errors like:

[10:35:54:483] kafka_connect: WARN: Failed to connect to Kafka. Retrying in 80 seconds
[10:35:54:575] kafka_error_callback: ERROR: Local: Broker transport failure (-195): riddler.caida.org:9092/bootstrap: Connect to ipv4#198.202.104.117:9092 failed: Connection refused
[10:35:54:575] kafka_connect: WARN: Failed to connect to Kafka. Retrying in 80 seconds
[10:35:54:601] kafka_error_callback: ERROR: Local: Broker transport failure (-195): penguin.caida.org:9092/bootstrap: Connect to ipv4#198.202.104.116:9092 failed: Connection refused
[10:35:54:601] kafka_connect: WARN: Failed to connect to Kafka. Retrying in 80 seconds
[10:35:54:757] kafka_error_callback: ERROR: Local: Broker transport failure (-195): penguin.caida.org:9092/bootstrap: Connect to ipv4#198.202.104.116:9092 failed: Connection refused
[10:35:54:757] kafka_error_callback: ERROR: Local: Broker transport failure (-195): riddler.caida.org:9092/bootstrap: Connect to ipv4#198.202.104.117:9092 failed: Connection refused
[10:35:54:757] kafka_connect: WARN: Failed to connect to Kafka. Retrying in 80 seconds

[alistairking]

It should only be a fatal error if all bootstrap servers are unreachable