Add curl to ironic-agent package installs
Add curl to ironic-agent package installs

The script for ironic-agent utilizes curl, however an extremely
minimal system may not have it, and as such we should list it as
a package that must be installed to support the element.

Change-Id: Id118f84e2d5e6adf0ae3d653864565368b0d76bf

takahashinobuyuki/diskimage-builder,takahashinobuyuki/diskimage-builder,switch-ch/diskimage-builder,CSC-IT-Center-for-Science/diskimage-builder,switch-ch/diskimage-builder,zioproto/diskimage-builder,zioproto/diskimage-builder,openstack/diskimage-builder,openstack/diskimage-builder,CSC-IT-Center-for-Science/diskimage-builder