Improve doc about installing and booting Fuel

user-guide
- initialize-fuel/0400-pxe-config -- added note that changing IP here changes CIDR
- initialize-fuel/0500-boot-fuel -- made this a top-level header
  - Added instructions for using a second NIC to access Fuel UI
- initialize-fuel/0600-boot-nodes -- made this a top-level header
  - Modified the instructions to log into the Fuel console to "if you have not already"

- 2000-deploy-environment
  - created an "Install Fuel" subsection and pulled together the pieces
    that were scattered through the next couple of sections.  A couple
    of the subsections were superfluous so I deleted those headers.
  - Added instructions to set the boot order with the hard drive
  - Added instructions to remove the installation media after installation completes
  - Moved the include line for 0400-pxe-config to the end of "Install"
  - Deleted "Initialize Fuel" and the table of steps --it just added an
    unnecessary level of complexity
  - Modified the instructions at the beginning of "Create Environment"
    to reflect that they should have already logged in

Change-Id: I99b01611bf6b6efef457469e442b49ef5bcfbef0