e2e tests: clean up antihelpful BeTrue()s

Many ginkgo tests have been written to use this evil form:

    GrepString("foo")
    Expect(that to BeTrue())

...which yields horrible useless messages on failure:

    false is not true

Identify those (automatically, via script) and convert to:

    Expect(output to ContainSubstring("foo"))

...which yields:

    "this output" does not contain substring "foo"

There are still many BeTrue()s left. This is just a start.

This is commit 1 of 2. It includes the script I used, and
all changes to *.go are those computed by the script.
Commit 2 will apply some manual fixes.

Signed-off-by: Ed Santiago <santiago@redhat.com>

test/e2e/prune_test.go

@@ -153,8 +153,7 @@ var _ = Describe("Podman prune", func() {
 		session := podmanTest.Podman([]string{"images", "-a"})
 		session.WaitWithDefaultTimeout()
 		Expect(session).Should(Exit(0))
-		hasNone, _ := session.GrepString("<none>")
-		Expect(hasNone).To(BeTrue())
+		Expect(session.OutputToString()).To(ContainSubstring("<none>"))
 
 		// Nothing will be pruned.
 		session = podmanTest.Podman([]string{"image", "prune", "-f"})