Add system test for the northbound API in NEMO project.

Add system test for the northbound API in NEMO project.

The main test includes:
- Add predefined role of users, which inludes tenant and admin
- Add predefined node type and connection type
- register a user whose role is tenant (create a vn space)
- In this vn space, issue an intent, that is, create two nodes and one connection
between them.

TODO list:
- Use customized switch to consruct a physical topology
- Test the intent result on the physical network, such as, ping

Change-Id: I185447428fe6c5e78176a210687e6f1f48008cb3
Signed-off-by: Zhang Yali <zhangyali369@huawei.com>