Rename runapitests.bash to runapitests.sh and make it use /bin/sh

This is a simple POSIX shell script, so no need for the weird extension
or for the explicit use of /bin/bash

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>

runapitests.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/sh
 
 cleanup() {
     rm -f /etc/lxc/test-busybox.conf