This changes the test names to use the last component, which is
generally the test data file, in place of the 2nd component, which is
less unique.

Change-Id: I182ad1ffb59595a6579a6a87e07af6cb11036e93
Reviewed-on: https://boringssl-review.googlesource.com/15584
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>