Nova API gateway needs to finish two tasks for security group
functionality. One is to create security group in bottom pod if
it does not exist. Only when the user boot a server can we know
which pod to create the security group. The other one is to
handle default security group. We decide to replace the default
"remote group" rules with several "remote ip prefix" rules.
Each rule points to a CIDR of one of the project's subnets.
Since the collection of subnets may change, we need to update
bottom security group rules.
Currently these two tasks both run in synchronous way. For
better response time the second task can be implemented in
asynchronous way later.
Neutron plugin part for security group functionality will be
covered in next patch.
Change-Id: I1822ff16e3dfc2a89c34f7833adcc1ad1d952462
8c0e8276c3