TEST: Refactor cube_to_h5 to general fxn; add case
TEST: Refactor cube_to_h5 to general fxn; add case

Test function formerly for no-args cube_to_h5 case refactored
 to be a general runner, taking **kwargs to be passed to cube_to_h5
 and a sizes dict indicating the correct size comparisons.

Added trunc=2 case.

bskinn/h5cube