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
Add extra list server by status test

Add list server by shutoff status test
Add list server by error status test

Change-Id: Ica063797a954a71c0e4c206be08c3c5cf4c60163
Improve testing of list_extensions for compute

This commit takes the testing for list_extension from the volumes
extensions client and uses it for the compute testing of
list_extensions. This also fixes a skip decorator to use use
requires_ext instead of calling is_extension_enabled directly.

Change-Id: Id08f39e09df0aea0d3c8f507f421c82ddf32900f
Remove copyright from empty files

According to policy change in HACKING:
http://docs.openstack.org/developer/hacking/#openstack-licensing
empty files should no longer contain copyright notices.

Change-Id: I91ef63a07519723b0b499e21f4b11aea6bfee8d1
Closes-Bug: #1262424
Merge "Remove copyright from empty files"
Merge "Add extra list server by status test"
Merge "port admin/test_servers* into Nova V3 tests part2"
Merge "Improve testing of list_extensions for compute"