The LVM driver accepts a "lvm_share_export_ips"
option instead of "lvm_share_export_ip" since
the Pike release [1]. Let's drop support for this
option and cleanup compatibility code.
[1] Ib3594aa5d7751c829820fce830d87f6ceea6b049
Change-Id: Ifdeb470438c204cc6cc370517833cb2cab5b7822