Sets the plan parameter value to the def default

If a parameter in an added template is defined with a default, the
environment parameter that corresponds to it will be initialized
with this value. This is to facilitate the client views and setting
of a plan's configuration.

Change-Id: Ibf240b587aa012f7dd236b7d0b9ba643ae595418
Implements: blueprint tripleo-juno-tuskar-plan-rest-api
Merge "Sets the plan parameter value to the def default"