Write test for HDFMapDigiSISCrate for active BRD & no active channels

[rocco8773]

After issue #59 and PR #61, a test case needs to be written for HDFMapDigiSISCrate to test the scenario where the "SIS Crate" has an active/enabled board, but no active/enabled channels. This is a semi-common scenario during campaigns so users can record, "document" setups (see #59 (comment)). In order to achieve this, the FauxSISCrate will likely need the associated functionality added to it. The FauxSISCrate generates the faux HDF5 files that tests utilize to test functionality, and FauxSISCrate currently only lets you to active board-channel combos and not just boards.