zuul: run cinder-tempest-plugin tests too

Tests from cinder-tempest-plugin should work with the NFS backend as well, so run them too.

Unfortunately it is not possible to reuse the ‘full-integrated’ tox environment as it does not allow for additional regexps, so try to mimic it by explicitly listing the tests.

This change also pins devstack-plugin-nfs-tempest-full to NFS version vers=4.2 in combination with nconnect=4, which improves test stability by preventing stalls on large write operations.