Added support for choosing the MCI name

* Added support for choosing the MCI name. 
* The logic added not just looks at the MCIs in a ServerTemplate. It looks at the MCIs in the account so the MCI can be overridden if the ST doesn't have the Blueskies supported MCI.
* If the MCI name is not provided, the default MCI in the ST will be chosen.
* Enhanced the `create_server` test to test both cases where the MCI name is provided as well as the default MCI is chosen.
* Enabled the pending tests corresponding to this mci param