perf-lib.sh: rely on test-lib.sh for --tee handling

perf-lib.sh: rely on test-lib.sh for --tee handling

Since its inception, the perf-lib.sh script has manually handled the
"--tee" option (and other options which imply it, like "--valgrind")
with a cut-and-pasted block from test-lib.sh. That block has grown stale
over the years, and has at least three problems:

  1. It uses $SHELL to re-exec the script, whereas the version in
     test-lib.sh learned to use $TEST_SHELL_PATH.

  2. It does an ad-hoc search of the "$*" string, whereas test-lib.sh
     learned to carefully parse the arguments left to right.

  3. It never learned about --verbose-log (which also implies --tee),
     so it would not trigger for that option.

This last one was especially annoying, because t/perf/run uses the
GIT_TEST_OPTS from your config.mak to run the perf scripts. So if you've
set, say, "-x --verbose-log" there, it will be passed as part of most
perf runs. And while this script doesn't recognize the option, the
test-lib.sh that we source _does_, and the behavior ends up being much
more annoying:

  - as the comment at the top of the block says, we have to run this
    tee code early, before we start munging variables (it says
    GIT_BUILD_DIR, but the problematic variable is actually
    GIT_TEST_INSTALLED).

  - since we don't recognize --verbose-log, we don't trigger the block.
    We go on to munge GIT_TEST_INSTALLED, converting it from a relative
    to an absolute path.

  - then we source test-lib.sh, which _does_ recognize --verbose-log. It
    re-execs the script, which runs again. But this time with an
    absolute version of GIT_TEST_INSTALLED.

  - As a result, we copy the absolute version of GIT_TEST_INSTALLED into
    perf_results_prefix. Instead of writing our results to the expected
    "test-results/build_1234abcd.p1234-whatever.times", we instead write
    them to "test-results/_full_path_to_repo_t_perf_build_1234...".

    The aggregate.perl script doesn't expect this, and so it prints
    "<missing>" for each result (even though it spent considerable time
    running the tests!).

We can solve all of these in one blow by just deleting our custom
handling, and relying on the inclusion of test-lib.sh to handle --tee,
--verbose-log, etc.

There's one catch, though. We want to handle GIT_TEST_INSTALLED after
we've included test-lib.sh, since we want it un-munged in the re-exec'd
version of the script. But if we want to convert it from a relative
to an absolute path, we must do so before we load test-lib.sh, since it
will change our working directory. So we compute the absolute directory
first, store it away, then include test-lib.sh, and finally assign to
GIT_TEST_INSTALLED as appropriate.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>