Skip fix_db_cache settings test due to a bug

Due to http://projects.theforeman.org/issues/8053 foreman-tasks are
being killed and if the fix_db_cache setting is true foreman-tasks does
not start and make the system not behave as expected.
Merge pull request #1617 from elyezer/skip-ui-settings-test

Skip fix_db_cache settings test due to a bug