virttest.utils_test.libvirt: Add a 'session' param to mk_part()

So we can use the same function to create a partition
on remote systems.

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
virttest.utils_test.libvirt: Set selinux to permissive in NFS tests

So that files in NFS can be accessed freely.

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
Merge pull request #1525 from autotest/utils-test-libvirt

Utils test libvirt