Added a new API extension
``security-groups-rules-belongs-to-default-sg`` that adds a new
read only field ``belongs_to_default_sg`` in the security group
rules. This flag determines if this security group rule belongs
to the project's default security group.
Related-Bug: #2019960
Change-Id: Ibd8f57d82b28f5cdb8874f1ae22cb35adcd8e880