Followup patch to rephrase 'cloud-backed' to indicate that
sushy-emulator is backed by libvirt or OpenStack cloud.
Change to use 'emulator' instead of 'simulator' across the docs.
As these emulators are used to substitute real Redfish BMC and
work to have same input/output as Redfish BMC, 'emulator' is the
term to use.
Change-Id: Ic2ca3f4d6b485085d1fc0300f5e697ac0473982f
44c4ad3787