Add lumiMask to masked blocks, fix unit tests for DBS3

In adding a lumi mask to Block.maskedBlocks, I discovered that all of the unit tests for Block_t.py were using an emulation of DBS2 which is not so useful anymore. This patch supplies a minimal emulation of DBS3 but in the end does not use it, instead using real DBS3 queries. 

I turned off some unit tests that don't seem to make sense with the workflows we have (parents of RAW files) but I left one failure in: testRunWhitelist fails because runLumi does work with DBS3. I can't tell if that really matters.

Adapt to full lumi list returned in maskedBlocks
New tests for lumi masks, remove existing which fails with DBS2 emulator
Simple emulator for DBS3. Incomplete.
Switch to real DBS, not emulator. Switch to a smaller RAW dataset