xenapi: Speed up tests by not waiting on conductor

Part of testing the xenapi agent code requires creating faults. This is
usually sent to the conductor to add to the database, but no conductor
is running during the tests. This results in waiting for a 15 second
timeout for every test that does this.

Disabling use of the conductor during these tests shaves about 45 seconds
off that is spent waiting on a reply that will never come.

Before:
    test_spawn_agent_upgrade_fails_silently  OK  15.20
    test_spawn_fails_agent_not_implemented   OK  15.18
    test_spawn_fails_with_agent_bad_return   OK  15.17

After:
    test_spawn_agent_upgrade_fails_silently  OK  0.16
    test_spawn_fails_agent_not_implemented   OK  0.18
    test_spawn_fails_with_agent_bad_return   OK  0.18

Change-Id: I31fedf6710aba3778eca694b45aabcffe4d09133
Merge "xenapi: Speed up tests by not waiting on conductor"