Rework the ironic-inspector auto-discovery test

Currently this test relies on changing the driver in introspection rules.
This is quite fragile, since for hardware types changing the driver may
involve changing some or all of the interface fields. It's also absolutely
unnecessary to verify the functioning of the discovery process.
This change removes it.

Instead, the change starts verifying the "auto_discovered" flag in
the introspection data, as well as uses introspection rules to verify
it indirectly.

Finally, the discovery driver is checked. The expected value is provided
by the new configuration option auto_discovery_default_driver.

Change-Id: Ia0e95cbc1bb4dbd32793705b876ab8b474b753ad
2 files changed