When the generic driver extends or shrinks a share it disables access
to the share by removing its export. Currently it uses the command
``exportfs -u local_path`` to do so, but this fails with current nfs
packages.
Fix the error by calling ``exportfs -u host:local_path`` instead.
Change-Id: Ic489a1607bf82964bf2859e89b3da1f572436d17
Closes-Bug: #1649782