Delete subnet fails if assoc port has IPs from another subnet

This change fixes the following failure scenario:
- Create a network
- Create two subnets on the network
- Create a port on the network using one of the subnets
- Delete the other subnet
= = = > FAILURE: Subnet delete fails because supposedly there
is/are port(s) still associated with that subnet.

The problem addressed is that delete_subnet() in
neutron/db/db_base_plugin.py is checking for port(s) still being
associated with the subnet's network, not the subnet itself.

Change-Id: I7adbe18cce412135b2e42dcb7c592e60c1ec5f8f
Closes-Bug: #1281694
UT: do not hide an original error in test resource ctxtmgr

In unit tests, resource contextmanagers such as network(), subnet()
try to delete themselves after returning from yield even if an
exception occurs. However when an exception occurs, there is a case
where deletion fails. In this case original exception will be hidden
and it makes difficult to debug test failures.

Before each test starts, resources like database entries will be
recreated, so there is no need to try to delete resources even
when an exception occurs. This commit removes try-finally clause
from resource contextmanagers to make original errors visible.

Closes-Bug: #1295887
Change-Id: Ia844d2aa2c9fc036e643068c5284f64798963ee3
Add missing parameters for port creation

Recent API changes in N1KV controller require parameters such as
subnet id and IP address to handle port creation successfully.
Without these mandatory paramters, the REST call fails.
This patch addresses that by passing in the missing parameters
in the REST body.

Change-Id: I4cec6868051f492b9d1245ab201ff6c1a0837848
Closes-Bug: #1290561
Merge "UT: do not hide an original error in test resource ctxtmgr"
Merge "Add missing parameters for port creation"
Merge "Delete subnet fails if assoc port has IPs from another subnet"