Increment attempt number instead of decrement when joining a consumer group

[mjparrott]

Two things this fixes:

1. The output of Unable to join consumer group "consumer_group". Will sleep 1 second and try again (attempt number x) should be less confusing, as it would start to become a negative number.

2. attempt_number is used to raise an error when @max_join_retries is reached. This would never be reached when attempt_number is decrementing.

[joshuawscott]

Makes sense to me. I kicked travis to fix the one test. I'll merge once it passes

[jbruggem]

Makes sense.

While you're at it, could you also maybe change the boundary check to be a bit more defensive ?

From :

if attempt_number == @max_join_retries do

To:

if attempt_number >= @max_join_retries do

[dantswain]

Great catch!

@jbruggem do you have any remaining concerns here?

[jbruggem]

@dantswain thanks for the reminder.