add open-iscsi to cloud image

I'm looking to reduce the number of differences between maas images (http://maas.ubuntu.com/images/ephemeral-v2/daily/) and which are built by lp:maas-images and cloud images .

One package difference is open-iscsi.

Add that to the cloud image. From a fresh wily instance:
$ sudo apt-get install open-iscsi
sudo: unable to resolve host wily-20151028-160214
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
  open-iscsi
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 271 kB of archives.
After this operation, 2,185 kB of additional disk space will be used

Thats larger than i'd like, but ability to do iscsi is nice.

Related bugs:
 * bug 1511006: move iscsi_ibft and iscsi_boot_sysfs to -virtual kernel