Extend test SetupMocks() to take arbitrary Canary resources

SetupMocks() currently takes a bool switch that tells it to configure
against either a shifting canary or an A-B canary.  I'll need a third
canary that has mirroring turned on so I changed this to an interface
that just takes the canary to configure (and configs the default
shifting canary if you pass nil).

pkg/controller/controller_test.go

@@ -42,11 +42,9 @@ type Mocks struct {
 	router        router.Interface
 }
 
-func SetupMocks(abtest bool) Mocks {
-	// init canary
-	c := newTestCanary()
-	if abtest {
-		c = newTestCanaryAB()
+func SetupMocks(c *v1alpha3.Canary) Mocks {
+	if c == nil {
+		c = newTestCanary()
 	}
 	flaggerClient := fakeFlagger.NewSimpleClientset(c)