Run with half the parallelism

Maybe 64 concurrent jobs is part of why we're getting flaky failures, at
least some of which look like timing issues.  Let's try half that.

Author: piki

integration-tests.sh

@@ -50,4 +50,5 @@ cd runtime_output_directory
 [ -e mysqld ] || ln -s mysqld-debug mysqld
 cd ../mysql-test
 export MTR_MAX_TEST_FAIL=1000
-./mysql-test-run --force --skip-ndb --nounit-tests --parallel=$(nproc)
+MTR_PARALLELISM=$[$(nproc) / 2]
+./mysql-test-run --force --skip-ndb --nounit-tests --parallel=$MTR_PARALLELISM