Add uuid to the NamespaceTask

This patch introduces an uuid to the
NamespaceTask class in order to use it
for the map between task and svc_instance.

The aim of this change is fix potential
concurrency issue.

Change-Id: I036dcd13357b4539d6d303610f5e9d44d65a2790
Merge "Add uuid to the NamespaceTask"