Update builtins to implement seed(s) function

builtin/myplugin/command/host.go

@@ -50,13 +50,18 @@ func (c *Host) Execute(trm terminal.UI, project core.Project) int32 {
 	h, err := project.Host()
 	if err != nil {
 		trm.Output("ERROR: %s", err)
+		return 1
 	}
 
+	trm.Output("have host plugin to run against")
+
 	if r, err := h.HasCapability("dummy"); !r {
 		trm.Output("No dummy capability found (%s)", err)
 		return 1
 	}
 
+	trm.Output("host plugin has dummy capability to run")
+
 	result, err := h.Capability("dummy", trm, "test value")
 	if err != nil {
 		trm.Output("Error running capability: %s", err)

builtin/myplugin/host/alwaystrue.go

@@ -16,6 +16,14 @@ type AlwaysTrueHost struct {
 	config HostConfig
 }
 
+func (c *AlwaysTrueHost) Seed(args ...interface{}) error {
+	return nil
+}
+
+func (c *AlwaysTrueHost) Seeds() ([]interface{}, error) {
+	return nil, nil
+}
+
 // DetectFunc implements component.Host
 func (h *AlwaysTrueHost) HostDetectFunc() interface{} {
 	return h.Detect

builtin/otherplugin/guest/alwaystrue.go

@@ -16,6 +16,14 @@ type AlwaysTrueGuest struct {
 	config GuestConfig
 }
 
+func (c *AlwaysTrueGuest) Seed(args ...interface{}) error {
+	return nil
+}
+
+func (c *AlwaysTrueGuest) Seeds() ([]interface{}, error) {
+	return nil, nil
+}
+
 // DetectFunc implements component.Guest
 func (h *AlwaysTrueGuest) GuestDetectFunc() interface{} {
 	return h.Detect