[2.2, trunk, UI] Unable to change device IP because 'subnet' is listed incorrectly on 'edit'.

[Andres Rodriguez]

I was trying to update the IP I gave to a device, and while doing so via the WebUI, I was unable to and no error was surfaced.

1. I added a device with IP 10.90.90.2.
2. I went to the device details page, interface section. And it lists:

MAC IP Assignment Subnet IP Address
aa:bb:cc:dd:ee:ff Static 10.90.90.0/24 10.90.90.2

3. I click on the interface to 'edit' it, and the following shows:
IP Assignment: Static
Subnet: 192.168.1.0/24
IP Address: 10.90.90.2

4. Obviously, I didn't notice that the 'Subnet' was automatically changed on edit, which caused the following error while trying to save. (I'll file a different bug for the lack of error surface).

Traceback (most recent call last):
  File "/usr/lib/python3.5/threading.py", line 862, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 824, in worker
    return target()
  File "/usr/lib/python3/dist-packages/twisted/_threads/_threadworker.py", line 46, in work
    task()
  File "/usr/lib/python3/dist-packages/twisted/_threads/_team.py", line 190, in doWork
    task()
--- <exception caught here> ---
  File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 246, in inContext
    result = inContext.theWork()
  File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 262, in <lambda>
    inContext.theWork = lambda: context.call(ctx, func, *args, **kw)
  File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 118, in callWithContext
    return self.currentContext().callWithContext(ctx, func, *args, **kw)
  File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 81, in callWithContext
    return func(*args,**kw)
  File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 857, in callInContext
    return func(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 225, in wrapper
    result = func(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/maasserver/utils/orm.py", line 685, in call_within_transaction
    return func_outside_txn(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/maasserver/utils/orm.py", line 503, in retrier
    return func(*args, **kwargs)
  File "/usr/lib/python3.5/contextlib.py", line 30, in inner
    return func(*args, **kwds)
  File "/usr/lib/python3/dist-packages/maasserver/websockets/handlers/device.py", line 350, in update_interface
    self._configure_interface(interface, params)
  File "/usr/lib/python3/dist-packages/maasserver/websockets/handlers/device.py", line 303, in _configure_interface
    INTERFACE_LINK_TYPE.STATIC, subnet, ip_address=ip_address)
  File "/usr/lib/python3/dist-packages/maasserver/models/interface.py", line 956, in link_subnet
    alloc_type=alloc_type, user=user)
  File "/usr/lib/python3/dist-packages/maasserver/models/interface.py", line 879, in _link_subnet_static
    "IP address is not in the given subnet '%s'." % subnet)
maasserver.exceptions.StaticIPAddressOutOfRange: IP address is not in the given subnet '192.168.1.0/24:192.168.1.0/24(vid=0)'.