InterfaceManagerConfigurationTest newl2vlanInterfaceTests is unstable

InterfaceManagerConfigurationTest newl2vlanInterfaceTests is unstable and occassional fails on the build servers, sometimes in merge and sometimes in verify jobs, recent examples:

https://jenkins.opendaylight.org/releng/job/genius-merge-fluorine/108/consoleFull#1624813939e5f83968-6a6e-4afa-aebf-7456048eb3ce (that was a merge job for https://git.opendaylight.org/gerrit/#/c/70445/)

https://jenkins.opendaylight.org/releng/job/genius-maven-verify-fluorine-mvn33-openjdk8/338/console (that was a verify job for https://git.opendaylight.org/gerrit/#/c/67468/)