Make api_samples reboot test use a plausible scenario

The idiot that wrote this test (me) implemented an invalid
sequence of events where a soft reboot follows a hard reboot,
which isn't allowed. I think the only reason this was passing
was because the instance dict in the api gets copied enough
times to avoid actually accounting for the state properly.

With the forthcoming objects patch, the accounting is tighter
and this impossibility gets caught.

Related to blueprint compute-api-objects

Change-Id: I7d08025df6f7895c97f84e8929a551ddede9f9ad