trivial: Show a warning when a requested plugin is not loaded
trivial: Show a warning when a requested plugin is not loaded

vathpela/fwupd,fwupd/fwupd,fwupd/fwupd,hughsie/fwupd,hughsie/fwupd,hughsie/fwupd,vathpela/fwupd,fwupd/fwupd,superm1/fwupd,fwupd/fwupd,vathpela/fwupd,hughsie/fwupd,superm1/fwupd,vathpela/fwupd,superm1/fwupd