server status remained in unexpected state

Two test case in the test_servers_negative change the 'one' servers
into a stable not active state. We are waiting 2 times 400 sec for
getting active state in vain.
Having those test cases to restore the expected state.

The deleted server related rebuild and reboot test case create are
merged and it creates and deletes one server.

Change-Id: Ie1b9dc62bad2bf7b8595da2c9d6f994c646a0025
Changed the exception name

Here changed the exception name for
http error code 409 from Duplicate to Conflict
and error code 500 from ComputeFault to ServerFault.

Change-Id: Ifbebd8761ac8402308e9d37ec78468c65539ac1a