fu-tool: Show errors if unable to access directory
fu-tool: Show errors if unable to access directory

When running in the sandbox this will make it more apparent why files
couldn't be opened.

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