perf testsuite: Add common output checking helper

As a form of validation, it is a common practice to check the outputs
of commands whether they contain expected patterns or match a certain
regular expression.

This output checking helper is designed to allow checking stderr output
of perf commands for unexpected messages, while ignoring messages that
are known to be harmless, e.g.:
"Lowering default frequency rate to \d+\."
"\d+ out of order events recorded."
etc.

Signed-off-by: Veronika Molnarova <[e-mail]>
Cc: Athira Rajeev <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Masami Hiramatsu <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Michael Petlan <[e-mail]>
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/tests/shell/common/check_errors_whitelisted.pl

···
+#!/usr/bin/perl
+# SPDX-License-Identifier: GPL-2.0
+
+$whitelist_file = shift;
+
+if (defined $whitelist_file)
+{
+	open (INFILE, $whitelist_file) or die "Checker error: Unable to open the whitelist file: $whitelist_file\n";
+	@regexps = <INFILE>;
+	close INFILE or die "Checker error: Unable to close the whitelist file: $whitelist_file\n";
+}
+else
+{
+	@regexps = ();
+}
+
+$max_printed_lines = 20;
+$max_printed_lines = $ENV{TESTLOG_ERR_MSG_MAX_LINES} if (defined $ENV{TESTLOG_ERR_MSG_MAX_LINES});
+
+$quiet = 1;
+$quiet = 0 if (defined $ENV{TESTLOG_VERBOSITY} && $ENV{TESTLOG_VERBOSITY} ge 2);
+
+$passed = 1;
+$lines_printed = 0;
+
+while (<STDIN>)
+{
+	s/\n//;
+
+	$line_matched = 0;
+	for $r (@regexps)
+	{
+		chomp $r;
+		if (/$r/)
+		{
+			$line_matched = 1;
+			last;
+		}
+	}
+
+	unless ($line_matched)
+	{
+		if ($lines_printed++ < $max_printed_lines)
+		{
+			print "Line did not match any pattern: \"$_\"\n" unless $quiet;
+		}
+		$passed = 0;
+	}
+}
+
+exit ($passed == 0);