Prefer TAP::Harness over Test::Harness

TAP:Harness came along in perl 5.10.1, and since we claim to support
perl 5.10.0 in configuration and testing, we can only load it
conditionally.

The main reason to use TAP::Harness rather than Test::Harness is its
capability to merge stdout and stderr output from the test recipes,
which Test::Harness can't.  The merge gives much more comprehensible
output when testing verbosely.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3424)