Release changes for 2.1.0

[jdeathe]

• Updates elinks package to elinks-0.12-0.37.pre6.el7.0.1.
• Updates source image to 2.5.1.
• Updates and restructures Dockerfile.
• Updates container naming conventions and readability of Makefile.
• Fixes issue with unexpected published port in run templates when DOCKER_PORT_MAP_TCP_80, DOCKER_PORT_MAP_TCP_443 or DOCKER_PORT_MAP_TCP_8443 is set to an empty string or 0.
• Fixes binary paths in systemd unit files for compatibility with both EL and Ubuntu hosts.
• Fixes link to OpenSSL ciphers manual page.
• Adds consideration for event lag into test cases for unhealthy health_status events.
• Adds port incrementation to Makefile's run template for container names with an instance suffix.
• Adds placeholder replacement of RELEASE_VERSION docker argument to systemd service unit template.
• Adds improvement to pull logic in systemd unit install template.
• Adds SSH_AUTOSTART_SUPERVISOR_STDOUT with a value "false", disabling startup of supervisor_stdout.
• Adds error messages to healthcheck script and includes supervisord check.
• Adds improved logging output.
• Adds images directory .dockerignore to reduce size of build context.
• Adds docker-compose configuration example.
• Adds improved lock/state file implementation between bootstrap and wrapper scripts.
• Adds graceful stop signals the supervisord configuration for httpd-wrapper.
• Removes use of /etc/services-config paths.
• Removes the unused group element from the default container name.
• Removes the node element from the default container name.
• Removes unused environment variables from Makefile and scmi configuration.
• Removes X-Fleet section from etcd register template unit-file.
• Removes unnecessary configuration file /etc/httpd-bootstrap.conf.
• Removes systemd health reporting from PHP-FPM configuration.
• Removes unnecessarily setting random passwords for system accounts during bootstrap; lock instead.
• Removes requirement for /usr/sbin/httpd-startup.