e2e: Cover RunnerDeployment (#668)

Previously the E2E test suite covered only RunnerSet. This refactors the existing E2E test code to extract the common test structure into a `env` struct and its methods, and use it to write two very similar tests, one for RunnerSet and another for RunnerDeployment.

testing/random.go

@@ -0,0 +1,21 @@
+package testing
+
+import (
+	"math/rand"
+	"time"
+)
+
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}
+
+const letterBytes = "abcdefghijklmnopqrstuvwxyz"
+
+// Copied from https://stackoverflow.com/a/31832326 with thanks
+func RandStringBytesRmndr(n int) string {
+	b := make([]byte, n)
+	for i := range b {
+		b[i] = letterBytes[rand.Int63()%int64(len(letterBytes))]
+	}
+	return string(b)
+}