Hard code to PST8 [#140373273]

We cannot assume we are running in a special environment that is always
in -8 time zone without DST. Making such setting explicit to make tests
portable.

Unskipping test as they will succeed now.

src/test/tinc/tincrepo/dml/functional/sql/changedistpolicy_dml_pttab_timestamptz.sql

@@ -5,7 +5,6 @@
 -- @product_version gpdb: [4.3-]
 -- @optimizer_mode on	
 -- @description Tests for MPP-21090
--- @skip #140373273
 \echo --start_ignore
 set gp_enable_column_oriented_table=on;
 \echo --end_ignore

src/test/tinc/tincrepo/dml/functional/sql/changedistpolicy_dml_regtab_random_timestamptz.sql

@@ -5,7 +5,6 @@
 -- @product_version gpdb: [4.3-]
 -- @optimizer_mode on	
 -- @description Tests for MPP-21090
--- @skip #140373273
 \echo --start_ignore
 set gp_enable_column_oriented_table=on;
 \echo --end_ignore

src/test/tinc/tincrepo/dml/functional/sql/changedistpolicy_dml_regtab_timestamptz.sql

@@ -5,7 +5,6 @@
 -- @product_version gpdb: [4.3-]
 -- @optimizer_mode on	
 -- @description Tests for MPP-21090
--- @skip #140373273
 \echo --start_ignore
 set gp_enable_column_oriented_table=on;
 \echo --end_ignore

src/test/tinc/tincrepo/dml/functional/sql/colalias_dml_timestamptz.sql

@@ -5,7 +5,6 @@
 -- @product_version gpdb: [4.3-]
 -- @optimizer_mode on	
 -- @description Tests for MPP-21090
--- @skip #140373273
 \echo --start_ignore
 set gp_enable_column_oriented_table=on;
 \echo --end_ignore

src/test/tinc/tincrepo/dml/functional/sql/dml_boundary_timestamptz.sql

@@ -4,7 +4,6 @@
 -- @tags dml 
 -- @db_name dmldb
 -- @description test: Boundary test for timestamptz
--- @skip #140373273
 \echo --start_ignore
 set gp_enable_column_oriented_table=on;
 \echo --end_ignore

src/test/tinc/tincrepo/dml/functional/sql/setup/timezone.sql

+ALTER DATABASE dmldb SET timezone TO PST8;