Require at least one console for LXC domain

A domain without a console quietly dies soon after start,
because we try to set /dev/null as a controlling TTY
2014-10-30 15:10:59.705+0000: 1: error : lxcContainerSetupFDs:283 :
ioctl(TIOCSCTTY) failed: Inappropriate ioctl for device

Report an error early instead of trying to start it.

https://bugzilla.redhat.com/show_bug.cgi?id=1155410

src/lxc/lxc_container.c

@@ -2093,8 +2093,10 @@ static int lxcContainerChild(void *data)
         if (virAsprintf(&ttyPath, "%s/%s.devpts/%s",
                         LXC_STATE_DIR, vmDef->name, tty) < 0)
             goto cleanup;
-    } else if (VIR_STRDUP(ttyPath, "/dev/null") < 0) {
-            goto cleanup;
+    } else {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("At least one tty is required"));
+        goto cleanup;
     }
 
     VIR_DEBUG("Container TTY path: %s", ttyPath);

src/lxc/lxc_process.c

@@ -1144,6 +1144,12 @@ int virLXCProcessStart(virConnectPtr conn,
                                       vm->def, NULL) < 0)
         goto cleanup;
 
+    if (vm->def->nconsoles == 0) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                       _("At least one PTY console is required"));
+        goto cleanup;
+    }
+
     for (i = 0; i < vm->def->nconsoles; i++) {
         char *ttyPath;
         if (vm->def->consoles[i]->source.type != VIR_DOMAIN_CHR_TYPE_PTY) {