crypto: testmgr - identify test vectors by name rather than number

In preparation for fuzz testing algorithms against their generic
implementation, make error messages in testmgr identify test vectors by
name rather than index.  Built-in test vectors are simply "named" by
their index in testmgr.h, as before.  But (in later patches) generated
test vectors will be given more descriptive names to help developers
debug problems detected with them.
Signed-off-by: NEric Biggers <ebiggers@google.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>