Removing ex_ from the front of vps_parameters to avoid overwrites of ser...

The base rimu compute class has options in the create function that can set custom memory and disk values for a VPS. The problem is in the logic that looks to see if vps_parameters is in the data structure sent in the create api call. In the first block it looks to see if vps_parameters exists which is the correct naming. In the second one it looks for ex_vps_parameters, which will never exist. And then it re initializes vps_parameters which wipes the values set for memory in the previous block. This change fixes that.