Factor data out of _check_titles

The straight-line implementation style of this test method allows
inconsistencies in checking to creep in. Switch to a data-driven
approach.

This is similar to I8cd2be14f4338413854042031cf41da534c11dcb but not
identical because in Nova, extra subsections are allowed.

Change-Id: I17f08212517814c91db7fb6ba18499673dba7fad
Merge "Factor data out of _check_titles"