Fixes issue with checking whether ISO is passed
Fixes issue with checking whether ISO is passed

This patch fixes the issue if IRONIC_BUILD_DEPLOY_RAMDISK
is set to false and IRONIC_DEPLOY_ISO is passed then it
will not throw the error.

Change-Id: Ic95f6e75d51db5cb60098bb131698cf44e772366
Story: 2007002
Task: 37777

openstack/ironic,openstack/ironic