backfill tests: case-insensitive cred search

add test about get cred by name case-insensitively
rename test about find cred by name-like to indicate it's about case-insensitivity (following the naming pattern of other similar existing tests)
motivation: we are about to perform some DB query optimization in terms of how we do case-insensitive cred name search, so need to make sure we have clear test coverage on this area in:
- get cred by name (added in this commit)
- find cred by name-like (already covered, renamed in this commit to make clearer)
- delete by name (already covered)

cloudfoundry / credhub