Preferences CLI - should be able to take in properties files using XML Format

https://github.com/caskdata/cdap/pull/1390

Figure out if XML file upload makes sense since the backend supports only string-string key-value map. Instead uploading Properties file would be better since it gels well with the backend feature.

The PR referenced above was revoked since it introduced external dependency. This JIRA needs a discussion whether XML files should be supported since in the backend of Preferences, we support only simple Map<String, String>. Probably properties files are better suited for this instead of XML.

Bug not touched in 2 years. Resolving.