Added Riak 2.0 docs for disterl port limit

Made small cleanups and added the section for riak.conf settings used to
limit the range of ports available to disterl.  Removed note about epmd
after verifying that it was unnecessary
Used config filetypes for source code sections
Merge pull request #1047 from angrycub/enhancement/cv/sec_and_fw_2.0

Added Riak 2.0 docs for disterl port limit