Revert "Use -j4 for make unitest-check."

This reverts commit 5ca65bed. Seems we are not
ready for parallel compilation of unittests yet. CI failed with weird looking
errors.

concourse/scripts/compile_gpdb.bash

@@ -91,7 +91,7 @@ function build_gppkg() {
 function unittest_check_gpdb() {
   pushd ${GPDB_SRC_PATH}
     source ${GREENPLUM_INSTALL_DIR}/greenplum_path.sh
-    make GPROOT=/usr/local -s -j4 unittest-check
+    make GPROOT=/usr/local -s unittest-check
   popd
 }
 

concourse/scripts/compile_gpdb_open_source_centos.bash

@@ -59,7 +59,7 @@ function build_gpdb() {
 
 function unittest_check_gpdb() {
   pushd gpdb_src/src/backend
-    make -s -j4 unittest-check
+    make -s unittest-check
   popd
 }
 

concourse/scripts/compile_gpdb_open_source_ubuntu.bash

@@ -37,7 +37,7 @@ function build_gpdb() {
 }
 
 function unittest_check_gpdb() {
-  make -C gpdb_src/src/backend -s -j4 unittest-check
+  make -C gpdb_src/src/backend -s unittest-check
 }
 
 function export_gpdb() {