Bug 7601: Cleanup Elan instances when a network is deleted

Bug 7601: Cleanup Elan instances when a network is deleted

The following patch in Neutron[1] modifies the Network delete sequence.
Prior to a network delete event, we now see an update event that removes
the networkType. So, in delete event, when we try to check for the
networkType, it would be empty and there is an exception. Because of this,
elanInstances are not getting deleted. In this patch, we avoid the check
for networkType since the network itself would not be created in the first
place if its not a supported networkType.

[1] https://review.openstack.org/#/c/317358/

Change-Id: I349a51f4df666ef2c2912ee552f159b6af16de76
Signed-off-by: Sridhar Gaddam <sgaddam@redhat.com>