IPA incompatible with Centos7

[Julia Kreger]

IPA DIB explicitly expects scsi-target-utils [0] to install tgtd and tgtcli, however Centos7 does not have the package, and only packages ?targetcli?.

Ultimately this means files are not found when IPA is directed to offer up an iscsi target for the iscsi deploy interface.

This issue was discovered upon a user reporting attempting to setup a centos based overcloud using the iscsi deploy driver, and was only discovered after identifying a bug [1] in IPA. Upon extracting the deployment ramdisk image, we found that the utilities were just not present, as the package does not exist as defined by [0].

In a sense, this likely should be something purely addressed in Diskimage-builder's ironic-agent element.

[0] https://github.com/openstack/diskimage-builder/blob/master/diskimage_builder/elements/ironic-agent/pkg-map
[1] https://review.openstack.org/#/c/501386/