ONELAB2: use _onelabClient for ONELAB2 in GmshMessage

git-svn-id: https://geuz.org/svn/gmsh/trunk@20165 59c8cabf-10d6-4a28-b43f-3936b85956c4
git-svn-id: https://geuz.org/svn/gmsh/trunk@20166 59c8cabf-10d6-4a28-b43f-3936b85956c4