Fix test_create_instance_invalid_key_name

In test_create_instance_invalid_key_name, there were the duplicated
negative factors. One is nonexistent image-id, the other one is non-
existent keypair.
This patch removes nonexistent image-id for the test purpose.

Change-Id: I90ff4e9ca0eeb149aa0db7be2d171561586724e9
Merge "Fix test_create_instance_invalid_key_name"