CCBC-316: Provide per-node config timeout

This provides a more "Semantic" bootstrap timeout by ensuring we don't
wait too long for any particular node. Useful for weeding out offline
nodes.

Behavior/API Modifications:

- Adding new lcb_cntl for this setting
- Changing timers in bucketconfig to use config_node_timeout rather than
  config_timeout
- config_node_timeout is set to 2 seconds by default

Change-Id: I12326d67934047d40bd9519e322c01685564834c
Reviewed-on: http://review.couchbase.org/33130
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>