Move ifupdown2addons into ifupdown2 pacakge

Ticket: CM-3864
Reviewed By:
Testing Done: Tested build and install

open item:
- cleanup stale ifupdown2-addons package files

docs.addons/source/intro.rst

@@ -0,0 +1,21 @@
+python-ifupdown2-addons
+-----------------------
+
+The python-ifupdown2-addons package contains ifupdown2 addon modules.
+
+addon modules are responsible for applying interface configuration.
+The modules are installed under /usr/share/ifupdownmodules.
+
+Each module can declare its own set of supported attributes. Each module
+is passed the iface object (which is a representation of /etc/network/interfaces
+iface entry). Each module is also passed the operation to be performed.
+
+Example modules are /usr/share/ifupdownmodules/address.py,
+/usr/share/ifupdownmodules/bridge.py etc
+
+The order in which these modules are invoked is listed in 
+/var/lib/ifupdownaddons/addons.conf. There is a ifaddon utility in the works
+to better manage the module ordering.
+
+For details on how to add a module, see the api reference and development
+documentation.