Fix inconsistency in expected fails with --html2wt

An unexpected fail was occurring when the --html2wt flag alone was
present. This was the result of having the wrong prefix set during the
test run. It only worked because environment variables remained set
between test runs.

The patch moves switching the config prefix from convertWt2Html to
before each case is run. This fixes a test and updates the blacklist.

Honoring languages was introduced in 2bd38515af648d5cf5d76c1b7febbe2a125c58d8

Bug: 52046
Change-Id: Ia918539cf97a15b441e64e4a5b9d6dcd5a1ad783