Add a new section "Cluster Configuration" to the docs

Added a new section that is intended as a how-to for configuring a Bro
cluster (this section does not discuss cluster architecture or theory)
that is aimed at beginners to Bro.  Most of this content was moved here
from the BroControl doc (which is now intended as more of a reference guide
for more experienced users) and the load balancing FAQ on the website.
Merge remote-tracking branch 'origin/master' into topic/dnthayer/ticket1186
Minor updates to cluster config docs

Incorporated some feedback from Jeannette, and temporarily removed
the PF_RING ZC section.
Minor update to cluster config docs

Forgot to add one small change in previous commit.
Merge remote-tracking branch 'origin/master' into topic/dnthayer/ticket1186
Update a broctl option name in cluster config doc
Update some doc tests and line numbers
Merge remote-tracking branch 'origin/topic/dnthayer/ticket1186'

* origin/topic/dnthayer/ticket1186:
  Update a broctl option name in cluster config doc
  Minor update to cluster config docs
  Minor updates to cluster config docs
  Add a new section "Cluster Configuration" to the docs
Merge remote-tracking branch 'origin/fastpath'

* origin/fastpath:
  Update some doc tests and line numbers