Use different database for fsyc, heap_checksum and walrep tests

Previously, fsyc, heap_checksum and walrep tests used separate
databases. But seems with merge when src/makefiles/pgxs.mk added
--dbname to REGRESS_OPTS, all of these tests started using
`contrib_regression` database even if each of these tests defined
--dbname=<>, it was overridden from src/makefiles/pgxs.mk.

Hence, set USE_MODULE_DB=1 which makes these tests to use
--dbname=$(CONTRIB_TESTDB_MODULE) instead of
`contrib_regression`. This way these will again start having separate
database.

src/test/fsync/Makefile

@@ -2,13 +2,14 @@ MODULES=fsync_helper
 PG_CONFIG=pg_config
 
 REGRESS = setup bgwriter_checkpoint
-REGRESS_OPTS = --dbname="fsync_regression" --load-extension=gp_inject_fault
+REGRESS_OPTS = --load-extension=gp_inject_fault
 
 subdir = src/test/fsync/
 top_builddir = ../../..
 
 include $(top_builddir)/src/Makefile.global
 
+USE_MODULE_DB=1
 NO_PGXS = 1
 include $(top_srcdir)/src/makefiles/pgxs.mk
 

src/test/heap_checksum/Makefile

@@ -2,13 +2,14 @@ MODULES=heap_checksum_helper
 PG_CONFIG=pg_config
 
 REGRESS = setup heap_checksum_corruption
-REGRESS_OPTS = --init-file=../regress/init_file --dbname="heap_checksum_regression" --load-extension=gp_inject_fault
+REGRESS_OPTS = --init-file=../regress/init_file --load-extension=gp_inject_fault
 
 subdir = src/test/heap_checksum/
 top_builddir = ../../..
 
 include $(top_builddir)/src/Makefile.global
 
+USE_MODULE_DB=1
 NO_PGXS = 1
 include $(top_srcdir)/src/makefiles/pgxs.mk
 

src/test/walrep/Makefile

@@ -8,8 +8,9 @@ include $(top_builddir)/src/Makefile.global
 
 REGRESS = setup
 REGRESS += replication_views_mirrored missing_xlog walreceiver generate_ao_xlog generate_aoco_xlog
-REGRESS_OPTS = --dbname="walrep_regression" --load-extension=gp_inject_fault
+REGRESS_OPTS = --load-extension=gp_inject_fault
 
+USE_MODULE_DB=1
 NO_PGXS = 1
 include $(top_srcdir)/src/makefiles/pgxs.mk