Elan interfaces are not always deleted after VM/port was deleted

Overview:
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In netvirt automated test we observed that some elan interfaces remains in the model after their related VMs/ports were deleted

For example:
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In the following jenkins job you can see that at the end of the serie of tests and after the VMs and ports are already deleted the elan interfaces still exist

https://logs.opendaylight.org/releng/jenkins092/netvirt-csit-1node-openstack-newton-nodl-v2-upstream-transparent-boron/446/archives/log.html.gz#s1-s1-s3

Look under:
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Test: Delete networks --> TEARDOWN --> KEYWORD : Get Model Dump --> For: @data models --> config/elan:elan-interfaces

As mentioned above, this issue was observed also during longevity test on a specific system and the none deletion of the elan interfaces caused system to be overloaded at some point