Use min_count to create servers in ListServersNegativeTestJSON

This is to use min_count=3 to create 3 servers, and then delete
one of the created servers, so to reduce the time of waiting for
one server to be active.

Besides, there is only one deleted server so needn't use a list,
thus the code can be more simple.

Change-Id: I1daabb64147bb9e0025ae7d7a0913254c966704f
1 file changed