[YARN-6393] Create a API class for yarn-native-service user-facing constants

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Component/s: yarn-native-services
• Target Version/s: yarn-native-services
• Assignee: Jian He
• Reporter: Jian He
• Created: 27/Mar/17 03:37
• Updated: 13/Sep/17 17:36
• Resolved: 13/Sep/17 17:36

Description

User can use some constants in the json input spec file for later substitution.
e.g. if user specifies $HOSTNAME in the env section of the input file, it'll be substituted by AM with the actual host name. We'll need to create an API class and clearly documents it.