Raise errors from #pipelined instead of returning them

[KJTsanaktsidis]

It seems redis-cluster-client intentionally decides to return errors from #pipelined, rather than raising them. I note that in #37 it was written:

In Grab’s Redis Cluster library, the function
Pipeline(PipelineReadOnly) returns a response with an error for
individual reply.
Instead of returning nil or an error message when err != nil, we could
check for errors for each result so successful queries are not affected.
This might have minimised the outage’s business impact.

I prefer the above behavior.

It's certainly true that returning the individual results from pipelined gives strictly more information than raising an exception. UNFORTUNATELY, redis-client chooses the opposite option; if any query caused an error, after processing the entire pipeline it raises rather than returns; see:
https://github.com/redis-rb/redis-client/blob/932c5e8909ede7575d56a117773be39f40e2da88/lib/redis_client/connection_mixin.rb#L60

I think consistency with redis-client is very valuable to have for redis-cluster-client, so I would suggest that changing the behaviour here (perhaps with a major version bump?) might be a good idea?

Alternatively, althought I think this would be even more confusing IMO, we could keep the error handling as-is here but patch it in redis-rb to raise instead of return.

[supercaracal]

Thank you for your pull request. Our redis-cluster-client aims behavior same as redis-client as possible. The error handling of pipelining might be changed in the future, but I'd say that it would be better to behave same now.