stage-1: retry mounting ZFS root a few times

This is a workaround for NixOS/nixpkgs#25383

nixos/modules/system/boot/stage-1-init.sh

@@ -370,12 +370,14 @@ mountFS() {
 
     mkdir -p "/mnt-root$mountPoint"
 
-    # For CIFS mounts, retry a few times before giving up.
+    # For ZFS and CIFS mounts, retry a few times before giving up.
+    # We do this for ZFS as a workaround for issue NixOS/nixpkgs#25383.
     local n=0
     while true; do
         mount "/mnt-root$mountPoint" && break
-        if [ "$fsType" != cifs -o "$n" -ge 10 ]; then fail; break; fi
+        if [ \( "$fsType" != cifs -a "$fsType" != zfs \) -o "$n" -ge 10 ]; then fail; break; fi
         echo "retrying..."
+        sleep 1
         n=$((n + 1))
     done