Test pt-upgrade host-to-host. Implement diff_query_times(). Export $test_diff from PerconaTest instead of doing diag() in no_diff().

lib/PerconaTest.pm

@@ -70,6 +70,7 @@ our @EXPORT      = qw(
    $dsn_opts
    $sandbox_version
    $can_load_data
+   $test_diff
 );
 
 our $trunk = $ENV{PERCONA_TOOLKIT_BRANCH};
@@ -82,6 +83,8 @@ eval {
 
 our $can_load_data = can_load_data();
 
+our $test_diff = '';
+
 our $dsn_opts = [
    {
       key  => 'A',
@@ -622,7 +625,7 @@ sub no_diff {
    }
 
    # diff the outputs.
-   my $out = `diff $res_file $cmp_file`;
+   $test_diff = `diff $res_file $cmp_file 2>&1`;
    my $retval = $?;
 
    # diff returns 0 if there were no differences,
@@ -630,7 +633,6 @@ sub no_diff {
    $retval = $retval >> 8; 
 
    if ( $retval ) {
-      diag($out);
       if ( $ENV{UPDATE_SAMPLES} || $args{update_sample} ) {
          `cat $tmp_file > $expected_output`;
          diag("Updated $expected_output");
@@ -642,11 +644,11 @@ sub no_diff {
       unless $ENV{KEEP_OUTPUT} || $args{keep_output};
 
    if ( $res_file ne $tmp_file ) {
-      1 while unlink $res_file;
+      unlink $res_file if -f $res_file;
    }
 
    if ( $cmp_file ne $expected_output ) {
-      1 while unlink $cmp_file;
+      unlink $cmp_file if -f $cmp_file;
    }
 
    return !$retval;