use grub/shim from host system

Also the boot method is now configured globaly as this is
the only way to make sure that unkonwn nodes get the right
stuff

Signed-off-by: Christian Goll <cgoll@suse.com>

internal/pkg/config/warewulf.go

@@ -10,4 +10,5 @@ type WarewulfConf struct {
 	EnableHostOverlay bool   `yaml:"host overlay" default:"true"`
 	Syslog            bool   `yaml:"syslog" default:"false"`
 	DataStore         string `yaml:"datastore" default:"/var/lib/warewulf"`
+	GrubBoot          bool   `yaml:"grubboot" default:"false"`
 }