DQUtils: Don't load oracle if unneeded.

Avoid loading the oracle module if it's not actually going to be used.

Fixes a test failure in DCSCalculator2 seen on el9. [The failure that was seen was due to an interface change in the sqlalchemy library used by the oracle module. I first tried fixing that up. But apparently the old interface would open the database collection lazily while the new interface would open it immediately. And opening the database connection to oracle didn't work. But the oracle connection wasn't actually used in this test, so rather than try to figure out what's going wrong with the oracle connection (which may just not work anymore due to DB changes), i just changed things so as not to load the oracle module if it's not needed. If it ever is actually needed, the sqlalchemy changes will still need to be dealt with.]

Fixes ATLASDQ-1106.