Update 'Introduction to Ironic' document

The first few sections of the 'Introduction to Ironic' document were updated to:
- mention that it is included with OpenStack releases starting with Kilo
- mention that Swift is missing from the Conceptual Architecture diagram
- removes Figure 1.3.1 "Deployment Architecture" and the text surrounding
  that for several reasons: it places ir-cond on the same host as n-cpu, which
  is not advisable in some situations; it suggests placing ir-api on a
  monolithic "Cloud Controller Node", but does not explain why this unusual
  choice was made; and it does not include any depiction of the physical
  servers which Ironic is going to manage, nor the IPMI network connectivity
  to them which is required.
- mentions that for security reasons, ir-cond should be placed on an isolated
  host, as it is the *only* service which requires access to both data plane
  and IPMI control plane.
- modified (what was Figure 1.3.2) deployment_architecture_2.png so that it
  doesn't include a figure number

Change-Id: Ifeeba636c9e7de65385e9f9c631709b2dd09e25b
Partial-Bug: #1353688
Merge "Update 'Introduction to Ironic' document"