fix erronous errTimedOut ("abandoned subscription...because consuming was taking too long")
fix erronous errTimedOut ("abandoned subscription...because consuming was taking too long")

The expiryTimer continues to run after msg is delivered to
child.messages. If <-child.feeder takes > MaxProcessingTime (which
depends on how fast the broker runs), the expiryTimer can expire
before we Reset() it. If this happens there is a message waiting
in expiryTimer.C which, if we don't clear it out, makes us think
the consumer stalled.

This is reproduced with a high traffic partition on a busy
broker, and measuring the time each line of the loop takes. The
>100ms stall is the <-child.feeder inside 'range child.feeder'.

raisemarketplace/sarama,vrischmann/sarama,vrischmann/sarama,mailgun/sarama,DataDog/sarama,Shopify/sarama,HelixEducation/sarama,VividCortex/sarama,VividCortex/sarama,raisemarketplace/sarama,remerge/sarama,Shopify/sarama,remerge/sarama,mailgun/sarama,HelixEducation/sarama,DataDog/sarama