fstests: Fix selection of NFSD export type for the pNFS test section

I noticed this task was unnecessarily triggered for non-NFS file
system types.

Reviewed-by: Luis Chamberlain <[email protected]>
Signed-off-by: Chuck Lever <[email protected]>

Author: chucklever

playbooks/roles/fstests/tasks/main.yml

@@ -748,6 +748,7 @@
   set_fact:
     fstests_nfs_export_fstype: "xfs"
   when:
+    - fstests_fstyp == "nfs"
     - fstests_nfs_section_pnfs|bool
 
 - name: Create NFS export for test vol