Explicitly SET gp_select_invisible to false instead of using RESET

As outlined in https://github.com/greenplum-db/gpdb/issues/685 we
have a problem with resetting GUCs in the backends when the GUC
was previously set in the per connection parameter. Explicitly set
this GUC to false since that's the intention with the RESET commands
in these cases to increase robustness of the tests.

src/test/regress/expected/qp_misc_jiras.out

@@ -1742,7 +1742,7 @@ WHERE T.SQ = 1
 (0 rows)
 
 drop table qp_misc_jiras.ins_cr_nds_dt, qp_misc_jiras.ins_cr_nds_mstr, qp_misc_jiras.m_ccr_cvr_nds_t99, qp_misc_jiras.m_ccr_mthy_cr_nds_t00;
-reset gp_select_invisible;
+set gp_select_invisible=false;
 create table qp_misc_jiras.tbl6448 (x "char");
 NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause -- Using column named 'x' as the Greenplum Database data distribution key for this table.
 HINT:  The 'DISTRIBUTED BY' clause determines the distribution of data. Make sure column(s) chosen are the optimal data distribution key to minimize skew.

src/test/regress/expected/qp_misc_jiras_optimizer.out

@@ -1739,7 +1739,7 @@ WHERE T.SQ = 1
 (0 rows)
 
 drop table qp_misc_jiras.ins_cr_nds_dt, qp_misc_jiras.ins_cr_nds_mstr, qp_misc_jiras.m_ccr_cvr_nds_t99, qp_misc_jiras.m_ccr_mthy_cr_nds_t00;
-reset gp_select_invisible;
+set gp_select_invisible=false;
 create table qp_misc_jiras.tbl6448 (x "char");
 NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause -- Using column named 'x' as the Greenplum Database data distribution key for this table.
 HINT:  The 'DISTRIBUTED BY' clause determines the distribution of data. Make sure column(s) chosen are the optimal data distribution key to minimize skew.

src/test/regress/sql/qp_misc_jiras.sql

@@ -1073,7 +1073,7 @@ WHERE T.SQ = 1
 
 drop table qp_misc_jiras.ins_cr_nds_dt, qp_misc_jiras.ins_cr_nds_mstr, qp_misc_jiras.m_ccr_cvr_nds_t99, qp_misc_jiras.m_ccr_mthy_cr_nds_t00;
 
-reset gp_select_invisible;
+set gp_select_invisible=false;
 
 create table qp_misc_jiras.tbl6448 (x "char");
 insert into qp_misc_jiras.tbl6448 values ('a');