libpod: Validate that log tag requires journald driver

Currently validation that log tag requires journald driver is done in several
places and emits only warning. Making it an error and moving to
`(c *Container) validate()` is a more correct approach.

Signed-off-by: Povilas Kanapickas <povilas@radix.lt>

test/e2e/logs_test.go

@@ -638,6 +638,12 @@ var _ = Describe("Podman logs", func() {
 		Expect(logc.OutputToString()).To(Equal("podman"))
 	})
 
+	It("log tag with non-journald driver fails", func() {
+		logc := podmanTest.Podman([]string{"run", "--log-driver", "k8s-file", "--log-opt", "tag=mytag", ALPINE, "true"})
+		logc.WaitWithDefaultTimeout()
+		Expect(logc).To(ExitWithError(125, "log tags can only be used with the journald log driver"))
+	})
+
 	It("podman pod logs with container names", func() {
 		SkipIfRemote("Remote can only process one container at a time")
 		podName := "testPod"