Set stop signal to 15 when not explicitly set

When going through the output of `podman inspect` to try and
identify another issue, I noticed that Podman 2.0 was setting
StopSignal to 0 on containers by default. After chasing it
through the command line and SpecGen, I determined that we were
actually not setting a default in Libpod, which is strange
because I swear we used to do that. I re-added the disappeared
default and now all is well again.

Also, while I was looking for the bug in SpecGen, I found a bunch
of TODOs that have already been done. Eliminate the comments for
these.

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

test/e2e/create_test.go

@@ -458,4 +458,17 @@ var _ = Describe("Podman create", func() {
 			Expect(session.ExitCode()).To(Equal(0))
 		}
 	})
+
+	It("podman create sets default stop signal 15", func() {
+		ctrName := "testCtr"
+		session := podmanTest.Podman([]string{"create", "--name", ctrName, ALPINE, "/bin/sh"})
+		session.WaitWithDefaultTimeout()
+		Expect(session.ExitCode()).To(Equal(0))
+
+		inspect := podmanTest.Podman([]string{"inspect", ctrName})
+		inspect.WaitWithDefaultTimeout()
+		data := inspect.InspectContainerToJSON()
+		Expect(len(data)).To(Equal(1))
+		Expect(data[0].Config.StopSignal).To(Equal(uint(15)))
+	})
 })