TS-2169 SSL Stats

Switched to pull request due to anticipated need to merge with more recent version of master in the future (when this gets pulled finally).

In addition to the stats already documented above, this also includes cipher stats.  Here's the excerpt from the traffic_line doc:

proxy.process.ssl.cipher.user_agent.{cipherName}
  Total number of ssl client connections that used cipherName.  The list of
  cipher stats is dynamic and depends upon the installed ciphers for the
  system.  Some common cipher stats are:
    proxy.process.ssl.cipher.user_agent.ECDHE-RSA-RC4-SHA
    proxy.process.ssl.cipher.user_agent.ECDHE-RSA-AES128-SHA256
    proxy.process.ssl.cipher.user_agent.ECDHE-RSA-AES128-GCM-SHA256
    proxy.process.ssl.cipher.user_agent.ECDHE-RSA-AES128-SHA
    proxy.process.ssl.cipher.user_agent.RC4-SHA
    proxy.process.ssl.cipher.user_agent.RC4-MD5
    proxy.process.ssl.cipher.user_agent.AES128-GCM-SHA256
    proxy.process.ssl.cipher.user_agent.AES128-SHA
  There are two ways to get the list of cipher stats:
  1.  Run ATS with debug logging and show ssl diags:
      CONFIG proxy.config.diags.debug.enabled INT 1
      CONFIG proxy.config.diags.debug.tags STRING ssl.*
      View output of traffic.out looking for lines like:
         (ssl) Registering ssl cipher stat 'proxy.process.ssl.cipher.user_agent.ECDHE-RSA-AES256-GCM-SHA384'
  2.  Run this script (just asks openssl to tell us):
         openssl ciphers | awk '{n=split($0,a,":"); for (i = 0; ++i <= n;) print "proxy.process.ssl.cipher.user_agent." a[i];}'