Reset queue_buffering_max_ms to default 1000 ms for varnishkafka

We increased this in attempt to avoid produce errors during
kafka <-> zookeeper timeouts.  However, this just caused
the number of buffered messages in varnishkafka to increase,
but did not actually help wtih produce errors.  As far as I can
tell currently, varnishkafka and librdkafka are not responsible
for lost messages during zookeeper timeouts.

https://commons.wikimedia.org/wiki/File:Esams_bits_varnishakfka_msgq_cnt.png
shows the msgq_cnt buffer
increase on esams bits since I started tweaking this setting.

You can read more about the bug we are trying to figure out here:
BUG 69667

Change-Id: If6a9d5e58c2917f2e37666ff6f70c44f2526ec15