PT-1554 Make QueryFormater consistent

In some OSes/Perl versions, the 'filtered' row is being printed with or
without decimals.
For example, in Ubuntu 16.04/Perl 5.22 it is 100.00 while in Ubuntu
18.04/Perl 5.26 it is 100.
To make it consistent for tests, add a default formating string for the
filtered row.

bin/pt-query-digest

@@ -7778,7 +7778,12 @@ sub explain_report {
             $explain .= "# *************************** $i. "
                       . "row ***************************\n";
             foreach my $j ( 0 .. $#row ) {
-               $explain .= sprintf "# %13s: %s\n", $sth->{NAME}->[$j],
+               # In some OSes/Perl versions, the filtered row can be reported with or without decimals.
+               # Example, in Ubuntu 16.04 it is being printed as 100.00 while in Ubuntu 18.04 it is
+               # being printed as 100.
+               # To make it testeable, we need to have a consistent format across versions.
+               my $value_format = $sth->{NAME}->[$j] eq 'filtered' ? "%.02f" : "%s";
+               $explain .= sprintf "# %13s: $value_format\n", $sth->{NAME}->[$j],
                   defined $row[$j] ? $row[$j] : 'NULL';
             }
             $i++;  # next row number

lib/QueryReportFormatter.pm

@@ -1332,7 +1332,8 @@ sub explain_report {
             $explain .= "# *************************** $i. "
                       . "row ***************************\n";
             foreach my $j ( 0 .. $#row ) {
-               $explain .= sprintf "# %13s: %s\n", $sth->{NAME}->[$j],
+               my $value_format = $sth->{NAME}->[$j] eq 'filtered' ? "%.02f" : "%s";
+               $explain .= sprintf "# %13s: $value_format\n", $sth->{NAME}->[$j],
                   defined $row[$j] ? $row[$j] : 'NULL';
             }
             $i++;  # next row number

t/pt-query-digest/samples/issue_1196-output-5.7.txt

@@ -45,7 +45,7 @@ select t.a, count(*) from t join t t2 using(a) group by 1 order by 2 desc limit
 #       key_len: NULL
 #           ref: NULL
 #          rows: 14
-#      filtered: 100
+#      filtered: 100.00
 #         Extra: Using temporary; Using filesort
 # *************************** 2. row ***************************
 #            id: 1
@@ -58,5 +58,5 @@ select t.a, count(*) from t join t t2 using(a) group by 1 order by 2 desc limit
 #       key_len: NULL
 #           ref: NULL
 #          rows: 14
-#      filtered: 10
+#      filtered: 10.00
 #         Extra: Using where; Using join buffer (Block Nested Loop)

t/pt-query-digest/samples/slow007_explain_1-57.txt

@@ -41,5 +41,5 @@ SELECT fruit FROM trees\G
 #       key_len: 27
 #           ref: NULL
 #          rows: 1
-#      filtered: 100
+#      filtered: 100.00
 #         Extra: Using index

t/pt-query-digest/samples/slow007_explain_2-57.txt

@@ -41,5 +41,5 @@ SELECT fruit FROM trees\G
 #       key_len: 27
 #           ref: NULL
 #          rows: 3
-#      filtered: 100
+#      filtered: 100.00
 #         Extra: Using index