QA: fix reimporting instance with different name

Since the original instance still exists, we need to use a different MAC
for its NIC.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>

qa/qa_instance.py

@@ -284,6 +284,7 @@ def TestInstanceImport(node, newinst, expnode, name):
   cmd = (['gnt-backup', 'import',
           '--disk-template=plain',
           '--no-ip-check',
+          '--net', '0:mac=generate',
           '--src-node=%s' % expnode['primary'],
           '--src-dir=%s/%s' % (constants.EXPORT_DIR, name),
           '--node=%s' % node['primary']] +