Return map parsed value at JsonParam.value

Currently, JsonParam returns String value as JsonParam.value.
However, SCHEMA_TYPES:MAP property doesn't support getting String value.
JsonParam have to return map value for to work properly.

Fixes bug #1256891

Change-Id: I5acc1aa95c0c0e7bebc760d8bf088971630696ec
Merge "Return map parsed value at JsonParam.value"