Include pg_test_timing's full output in the TAP test log.

Include pg_test_timing's full output in the TAP test log.

We were already doing a short (1-second) pg_test_timing run during
check-world and buildfarm runs.  But we weren't doing anything
with the result except for a basic regex-based sanity check.
Collecting that output from buildfarm runs is seeming very
attractive though, because it would help us determine what sort
of timing resolution is available on supported platforms.
It's not very long, so let's just note it verbatim in the TAP log.

Discussion: https://postgr.es/m/3321785.1758728271@sss.pgh.pa.us