Split up fu_engine_install() into two halves
Split up fu_engine_install() into two halves

No logic changes, just reshuffling.

fwupd/fwupd,fwupd/fwupd,fwupd/fwupd,hughsie/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd,hughsie/fwupd