Use min_count to create multi servers

When using min_count in test_create_server, it will not create and
wait for server active one by one, and thus will reduce the testcase's
excuting time.

Besides, we can wait for server active after all servers' create
requests are posted in order to save some time.

Change-Id: I68614a27249cc2b17ef6a2b909f01b56dfd6efe9
2 files changed