Yes, as I wrote at the start, I'm able to mount NFS manually.
Here is the results of the command you gave. [i did "cd" to the nfs share of
course] :
[root@luli-ovirt-01 nfs_ovirt_engine]# sudo -u vdsm mkdir test
[root@luli-ovirt-01 nfs_ovirt_engine]# ls
test
[root@luli-ovirt-01 nfs_ovirt_engine]#
it's working manually