Release changes for 2.6.1

[jdeathe]

• Deprecate Makefile target logs-delayed; replaced with logsdef.
• Updates openssh package to 7.4p1-21.el7.
• Updates openssl package to 1.0.2k-19.el7.
• Updates sudo package to 1.8.23-4.el7.
• Updates yum-plugin-versionlock package to 1.1.31-52.el7.
• Updates supervisord to 4.0.4.
• Updates test/health_status helper script with for consistency.
• Updates Makefile target logs to accept [OPTIONS] (e.g make -- logs -ft).
• Updates healthcheck script; state file existence confirms bootstrap completion.
• Updates system-timezone-wrapper to improve timer accuracy.
• Updates scripts to explicitly check for a file when handling lock/state files.
• Updates method used for returning current script.
• Updates info/error output for consistency.
• Updates healthcheck failure messages to remove EOL character that is rendered in status response.
• Updates wrapper script; only emit "waiting on" info message if bootstrap hasn't completed.
• Updates CHANGELOG.md to simplify maintenance.
• Updates README.md to simplify contents and improve readability.
• Updates README-short.txt to apply to all image variants.
• Updates Dockerfile org.deathe.description metadata LABEL for consistency.
• Updates ordering of Tags and respective Dockerfile links in README.md for readability.
• Adds improved test workflow; added test-setup target to Makefile.
• Adds Makefile target logsdef to handle deferred logs output within a target chain.
• Adds exec proxy function to sshd-wrapper used to pass through nice.
• Adds double quotes around value containing spaces.
• Adds /docs directory for supplementary documentation and simplify README.
• Fixes validation failure of 0 second --timeout value in test/health_status.
• Removes ENABLE_SSHD_BOOTSTRAP from docker-compose example configuration.
• Removes ENABLE_SSHD_WRAPPER from docker-compose example configuration.