We've had a bit of churn recently with regard to the unit test

infrastructure for SCMTools and in-progress changes. Very temporarily,

unit tests could get away with not using the test_scmtools fixture,

but only as an artifact of state leakage. Recent landed changes

therefore passed at the time without this fixture, but is needed with it

now, since we still need a Tool object in the database and we only do

this if test_scmtools is added.
This change adds this missing fixture to all tests that make use of

repositories/SCMTools.
It also fixes two other test failures.
One was due to a copy/paste of a bad logging.disable() line in a new

test, a copy of the problem fixed in commit 9f51ffeb3. This was causing

test_registry to fail if run after the bad call.
The other was due to a unit test using assertQueries() that wasn't

updated for a change in Review accessibility checks. This has

uncovered a duplicate Q(public=True) that may be a problem,

particularly when trying to use Q(public=False). This needs to be

thoroughly investigated before we ship 5.0, in case there are security

implications.
And finally, it disables warnings in test runs due to the empty content

in test_scmtools by preventing Django from trying to load data from

this fixture in setUpClass().

All unit tests pass.