rabbit: more precise iterconsume timeout

The iterconsume always set the timeout of kombu to 1 second
even the requested timeout more precise or < 1 second.

This change fixes that.

Related bug: #1400268
Related bug: #1399257

Change-Id: I157dab80cdb4afcf9a5f26fa900f96f0696db502
Merge "rabbit: more precise iterconsume timeout"