add server delete/unpause tests

add an expected behaviour test of deleting server
- delete_active_server
add two negative tests for server unpausing
- unpause_non_existent_server
- unpause_server_invalid_state

Change-Id: Ia9b5fdf1c2298ff685322fc99a5496710a7a67ef
Merge "add server delete/unpause tests"
TEMPEST_PY26_NOSE_COMPAT in py26 jobs

Use py26 skip exception compatibility code path in py26 jobs.

Change-Id: Id6c29f26f19f69abab558d5f94d8cbf6190ed43b