1145734 - more correct error message when apache fails

[BZ-1145734](https://bugzilla.redhat.com/show_bug.cgi?id=1145734) 

Suggesting that the user should run `pulp-manage-db` is often accurate but it can be a confusing message if the error is unrelated. New message provides context so the user will know if they need to run `pulp-manage-db`.
The reasons that pulp-manage-db may need to be run extends beyond just new types being added.  Anything from bug fixes to new platform (core) features or enhancements could introduce migrations.  Your language here should probably state that a possible cause is that pulp-manage-db needs to be run to migrate the DB to the latest version or to add new content type definitions introduced by newly installed plugins.