Create sized volume floc 978

Fixes FLOC-978
There are two cases to test so I think having two tests makes sense.  However, `test_create_filesystem` should probably be expanded to explicitly cover the size information.  This new test demonstrates that if you specify a particular size you get a volume with that size.  Some test should demonstrate that if you don't specify any size you get a volume with no particular size (that is, with a `VolumeSize(maximum_size=None)`).