Add depends_on field for core service ordering

* Adds depends_on fields to compose YAML
* Updates parsing code to copy across depends_on field to
openfaas service from compose service definition
* Adds algorithm and unit tests for finding order
* Applies order to up.go command
* Makes unit testing on MacOS possible through build directives

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

pkg/graph_test.go

@@ -0,0 +1,41 @@
+package pkg
+
+import "testing"
+
+func Test_RemoveMedial(t *testing.T) {
+	g := Graph{nodes: []*Node{}}
+	a := &Node{Name: "A"}
+	b := &Node{Name: "B"}
+	c := &Node{Name: "C"}
+
+	g.nodes = append(g.nodes, a)
+	g.nodes = append(g.nodes, b)
+	g.nodes = append(g.nodes, c)
+
+	g.Remove(b)
+
+	for _, n := range g.nodes {
+		if n.Name == b.Name {
+			t.Fatalf("Found deleted node: %s", n.Name)
+		}
+	}
+}
+
+func Test_RemoveFinal(t *testing.T) {
+	g := Graph{nodes: []*Node{}}
+	a := &Node{Name: "A"}
+	b := &Node{Name: "B"}
+	c := &Node{Name: "C"}
+
+	g.nodes = append(g.nodes, a)
+	g.nodes = append(g.nodes, b)
+	g.nodes = append(g.nodes, c)
+
+	g.Remove(c)
+
+	for _, n := range g.nodes {
+		if n.Name == c.Name {
+			t.Fatalf("Found deleted node: %s", c.Name)
+		}
+	}
+}