While Carbon takes less than a second [0], Nitrogen frequently takes more than 10 seconds [1] to accept a connection, causing test failures.

Karaf.log [2] shows the pause happens after "Generating host key" at 19:57:39,100.

[0] https://logs.opendaylight.org/releng/jenkins092/netconf-csit-1node-userfeatures-only-carbon/564/log.html.gz#s1-s3-s1-t1-k3-k1-k2
[1] https://logs.opendaylight.org/releng/jenkins092/netconf-csit-1node-userfeatures-only-nitrogen/115/log.html.gz#s1-s3-s1-t1-k3-k1-k2
[2] https://logs.opendaylight.org/releng/jenkins092/netconf-csit-1node-userfeatures-only-nitrogen/115/odl1_karaf.log.gz