Use fake images for machine tests

In tests that do not start a machine, we can use "fake" images to speed
up tests.  In the case of darwin and Linux, that can be /dev/null.  The
hypervisors don't care.

In the case of Windows, some research will need to be done to determine
the same approach but this is a start.

Signed-off-by: Brent Baude <bbaude@redhat.com>

pkg/machine/e2e/ssh_test.go

@@ -21,7 +21,7 @@ var _ = Describe("podman machine ssh", func() {
 	It("ssh to non-running machine", func() {
 		name := randomString()
 		i := new(initMachine)
-		session, err := mb.setName(name).setCmd(i.withImage(mb.imagePath)).run()
+		session, err := mb.setName(name).setCmd(i.withFakeImage(mb)).run()
 		Expect(err).ToNot(HaveOccurred())
 		Expect(session).To(Exit(0))