initramfs: ensure that /var/lib exists

In commit 74f7df68 files got moved from /etc/iscsi/nodes to /var/lib/iscsi to follow upstream changes.

Now when booting from a system with rootfs on iSCSI, it fails in initramfs stage, with:

  iscsistart: version 2.1.11
  iscsistart: Could not make /var/lib/iscsi 2
  iscsistart: exiting due to idbm configuration error

Ensure that the underlying /var/lib directory exists, so iscsistart can create /var/lib/iscsi etc as needed.

Thanks: Leon Blakey code@leonblakey.com

Closes: #1103644