Update component docs to refer to ironic-agent
Update component docs to refer to ironic-agent

The components documentation was previously referring to the
ramdisk image for deployment, which was previously deprecated.

Corrected to point to the ironic-agent element.

Change-Id: I770460041eb13523896aaadb7705bdc3db1a54ca

switch-ch/diskimage-builder,switch-ch/diskimage-builder,openstack/diskimage-builder,openstack/diskimage-builder