perf: fix when running with TEST_OUTPUT_DIRECTORY

When the TEST_OUTPUT_DIRECTORY is defined, then all test data will be
written in that directory instead of the default directory located in
"t/". While this works as expected for our normal tests, performance
tests fail to locate and aggregate performance data because they don't
know to handle TEST_OUTPUT_DIRECTORY correctly and always look at the
default location.

Fix the issue by adding a `--results-dir` parameter to "aggregate.perl"
which identifies the directory where results are and by making the "run"
script awake of the TEST_OUTPUT_DIRECTORY variable.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/perf/aggregate.perl

@@ -58,6 +58,7 @@ sub usage {
   Options:
     --codespeed          * Format output for Codespeed
     --reponame    <str>  * Send given reponame to codespeed
+    --results-dir <str>  * Directory where test results are located
     --sort-by     <str>  * Sort output (only "regression" criteria is supported)
     --subsection  <str>  * Use results from given subsection
 
@@ -91,11 +92,13 @@ sub sane_backticks {
 
 my (@dirs, %dirnames, %dirabbrevs, %prefixes, @tests,
     $codespeed, $sortby, $subsection, $reponame);
+my $resultsdir = "test-results";
 
 Getopt::Long::Configure qw/ require_order /;
 
 my $rc = GetOptions("codespeed"     => \$codespeed,
 		    "reponame=s"    => \$reponame,
+		    "results-dir=s" => \$resultsdir,
 		    "sort-by=s"     => \$sortby,
 		    "subsection=s"  => \$subsection);
 usage() unless $rc;
@@ -137,8 +140,6 @@ if (not @tests) {
 	@tests = glob "p????-*.sh";
 }
 
-my $resultsdir = "test-results";
-
 if (! $subsection and
     exists $ENV{GIT_PERF_SUBSECTION} and
     $ENV{GIT_PERF_SUBSECTION} ne "") {