The consumer loop is over engineered, it returns unused return,
iterconsume creates an iterator directly consumed by 'consume' without
special handling, and in some case kombu error callback are called when
the iterator is stopped and log useless error.
And in reality the consumer is always called when limit=1.
This change simplifies that, by removing the loop and removes all
returns stuffs.
Closes bug: #1450336
Change-Id: Ia2cb52c8577b29e74d4d2b0ed0b535102f2d55c7
6c91066c72