Fix test failure caused by making genconfig trackerless When I removed the need to have a tracker for genconfig, I broke a couple of tests. The breakage was hidden by a bad workflow. This change allows the tests to pass and refactors reporting of UsageError exceptions in admin.py. It also adds a test for failure in install command as there is a test case for it and this test tests the refactor.

def audit_html_files(db, cl, nodeid, newvalues):
    if 'type' in newvalues and newvalues['type'] == 'text/html':
        newvalues['type'] = 'text/plain'
    

def init(db):
    db.file.audit('set', audit_html_files)
    db.file.audit('create', audit_html_files)