fix(overlayfs): to allow overlay on top of network device (nfs)

Execute mount-overlayfs later in the boot process as a pre-pivot
hook. The existing mount hook is skipped for network boot.

Without this change
`dracut  -a "overlayfs nfs"`
would not work as expected.

Improved the existing test case to test for this scenario.

modules.d/90overlayfs/module-setup.sh

@@ -14,5 +14,6 @@ installkernel() {
 }
 
 install() {
-    inst_hook mount 01 "$moddir/mount-overlayfs.sh"
+    inst_hook mount 01 "$moddir/mount-overlayfs.sh"     # overlay on top of block device
+    inst_hook pre-pivot 10 "$moddir/mount-overlayfs.sh" # overlay on top of network device (e.g. nfs)
 }

test/TEST-20-NFS/client-init.sh

@@ -24,6 +24,13 @@ while read -r dev _ fstype opts rest || [ -n "$dev" ]; do
     break
 done < /proc/mounts
 
+# fail the test of rd.live.overlay did not worked as expected
+if grep -qF 'rd.live.overlay' /proc/cmdline; then
+    if ! strstr "$(cat /proc/mounts)" LiveOS_rootfs; then
+        echo "nfs-FAIL" | dd oflag=direct,dsync of=/dev/disk/by-id/ata-disk_marker
+    fi
+fi
+
 if [ "$fstype" = "nfs" -o "$fstype" = "nfs4" ]; then
 
     serverip=${dev%:*}