Compare the tuplevalue in question rather than saving full output

Rather than storing the full 100kb string in the outfile (which adds
200kb for the header) and passing to diff instead compare the tuple
with the expected value and store the boolean result in the outfile
instead.

This shaves 1.25 seconds off the testsuite on my laptop but the
primary win is to shrink the size of the outfiles. Tests on Pulse
show consistently lower diff times.

src/test/regress/sql/qp_misc_jiras.sql

@@ -2801,9 +2801,9 @@ insert into qp_misc_jiras.tbl13491_h values (1, lpad('a', 100000, 'b'));
 create table qp_misc_jiras.tbl13491_aocol with (appendonly=true, orientation=column) as select * from qp_misc_jiras.tbl13491_h distributed by (a);
 truncate table qp_misc_jiras.tbl13491_h;
 \t off
-select * from qp_misc_jiras.tbl13491_aocol;
+select str = lpad('a', 100000, 'b') from qp_misc_jiras.tbl13491_aocol;
 drop table qp_misc_jiras.tbl13491_h;
-select * from qp_misc_jiras.tbl13491_aocol;
+select str = lpad('a', 100000, 'b') from qp_misc_jiras.tbl13491_aocol;
 drop table qp_misc_jiras.tbl13491_aocol;
 -- start_ignore
 drop function if exists test();