port admin/test_servers* into Nova V3 tests part2

1. porting admin/test_servers.py and admin/test_servers_negative.py
   into nova v3
2. sync nova v2 changes in Ibd04a1fdaab74fe59bcf16cc99d4ecf4821f4ae2
3. fix a few typos in servers_client.py

Partially implements blueprint nova-v3-api-tests

Change-Id: I319bef11d1aee11ffa892c366cd57eef338b36ee
Closes-Bug: #1259056
Merge "port admin/test_servers* into Nova V3 tests part2"