Update compute rpcapi tests to use instance object instead of dict

Bugs such as 1327145 when the rpc code is accidentally reverted
to passing dicts instead of objects are not currently detected by
the unit tests because these are always called with a dict.

This change updates all compute rpcapi unit test cases to pass
an instance object to all cases where the version has been
converted to objects, so that such issues are now detected.

Related to blueprint compute-manager-objects-juno

Change-Id: I9b974e3a8e8e6dcbf87b1bdc854f05e94e7a35ce
Merge "Update compute rpcapi tests to use instance object instead of dict"