Only print what's needed for the safepoints test

(cherry picked from commit 36262c2)

Author: eregon

test/truffle/integration/safepoints.sh

@@ -1,15 +1,25 @@
 #!/usr/bin/env bash
 
 source test/truffle/common.sh.inc
+set +x
 
 if out=$(jt ruby test/truffle/integration/safepoints/exit_when_blocked.rb 2>&1); then
   echo "$out"
   echo "The script succeeded when it was expected to fail"
   exit 1
 else
-  # We do not want stacktraces of non-blocked threads
-  echo "$out" | grep -v "SafepointManager.step" >/dev/null
   # Stacktrace of the blocked thread
-  echo "$out" | grep "DeadBlockNode.deadBlock"
-  echo "$out" | grep "terminating the process"
+  if ! [[ "$out" == *"DeadBlockNode.deadBlock"* ]]; then
+    echo "No DeadBlockNode.deadBlock"
+    echo "$out"
+    exit 1
+  fi
+
+  if ! [[ "$out" == *"terminating the process"* ]]; then
+    echo "No 'terminating the process'"
+    echo "$out"
+    exit 1
+  fi
+
+  echo success
 fi