Move negative action tests to right place

Negative tests of server should be written on test_servers_negative.py,
but some negative tests are written on positive tests file, then that
would mislead developers who add new negative tests.

This patch moves these negative tests to a right place.

Change-Id: If3ddb2a0a5d27a87d610c6d8e7783d400fd32606
VPNaas vpnservice test cases

Adding testcases for vpn service create, list, delete, and show
part of blueprint: vpnaas-api-test-cases
Change-Id: I015fd503a198f93bfc7382e30b2aff5c74b3fd30
Merge "Move negative action tests to right place"
Merge "VPNaas vpnservice test cases"