Minimize stdout logging in pairwise testing jobs

Minimize stdout logging in pairwise testing jobs

The size of the log generated by each GitLab CI job is limited to 4 MB
by default.  While this limit is configurable, it makes little sense to
print build logs to standard output if they are being captured to files
anyway.  Limit use of "tee" in util/pairwise-testing.sh to printing the
combination of configure switches used for a given build.  This way the
job should never exceed the default 4 MB log size limit, yet it will
still indicate its progress in a concise way.