Expose target_uri on Task resource

The target_uri is used to identify which resource the Task is associated to.
It will be useful to update UI accordingly when a Task is running.
So if a user A starts a Task it will be shown to user B as a task in
progress.

Signed-off-by: Aline Manera <alinefm@linux.vnet.ibm.com>
Update current code to report target_uri while creating a Task

It will be useful to list Task by target_uri

Signed-off-by: Aline Manera <alinefm@linux.vnet.ibm.com>