TOSCA template Ouptut attributes

TOSCA service templates has an Output section which is used to display values of end user's interest. There is also implementation for it (i.e. parameters.py). However, as TOSCA spec evolves the output attributes can be used as an input to some other TOSCA service template or topology_template within a service template. At present, the 'value' keyword has been used to display string values of an attribute but it can be map or complex datatype which will need to process accordingly. This is a low priority work item for now and crated for tracking purpose.