Ensure that exception raised in neutron are handled correctly

We are now logging exceptions so we need to use save_and_reraise.

The patch set has also added log messages for exceptions that were
raised. This will be very helpful for debugging and troubleshooting.
This is done in the following cases:
 - unable to access a port when validating networks
 - unable to find a requested floating ip

Change-Id: I946126c2fb5aa229f917f8cb36ecb23aab528e14
Merge "Ensure that exception raised in neutron are handled correctly"