Attempt to allow lxc-attach to attach to running containers

lxc-attach.diff

diff -dpru lxc-2.0.9/src/lxc/tools/lxc_attach.c lxc-2.0.9.attach/src/lxc/tools/lxc_attach.c
--- lxc-2.0.9/src/lxc/tools/lxc_attach.c	2017-10-19 12:13:25.000000000 -0500
+++ lxc-2.0.9.attach/src/lxc/tools/lxc_attach.c	2017-10-25 14:41:27.263268277 -0500
@@ -431,8 +431,8 @@ int main(int argc, char *argv[])
 		exit(EXIT_FAILURE);
 	}

-	if (!c->is_defined(c)) {
-		fprintf(stderr, "Error: container %s is not defined\n", c->name);
+	if (!(c->is_defined(c) || c->is_running(c))) {
+		fprintf(stderr, "Error: container %s is not defined or running\n", c->name);
 		lxc_container_put(c);
 		exit(EXIT_FAILURE);
 	}