Add append_keyword field in logtrail.json

• Added new keyword_suffix field in logtrail.json. Specifies the keyword suffix to be appended for hostname & program fields. Set it to "" to not append any suffix.By default set to keyword. If not specified ( undefined) logtrail will append .keyword for backward compatibility.
• updated logtrail to load logtrail.json from file or ES during every launch instead of during startup.