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/runtime/runtime.go

@@ -0,0 +1,31 @@
+package runtime
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+type Cmdr struct {
+}
+
+func (k Cmdr) CombinedOutput(cmd *exec.Cmd) (string, error) {
+	o, err := cmd.CombinedOutput()
+	if err != nil {
+		args := append([]string{}, cmd.Args...)
+		args[0] = cmd.Path
+
+		cs := strings.Join(args, " ")
+		s := string(o)
+		k.Errorf("%s failed with output:\n%s", cs, s)
+
+		return s, err
+	}
+
+	return string(o), nil
+}
+
+func (k Cmdr) Errorf(f string, args ...interface{}) {
+	fmt.Fprintf(os.Stderr, f+"\n", args...)
+}