Blacklist tests under gcstress/debug/target.

Test: test.py --gcstress --target --debug
Change-Id: Ie1cbc80ac677fedc430f1d25830d1a555af42a67
diff --git a/test/knownfailures.json b/test/knownfailures.json
index 67ca316..8843dc8 100644
--- a/test/knownfailures.json
+++ b/test/knownfailures.json
@@ -710,5 +710,10 @@
         "description": [ "Tests require speed compilation which is no longer the default for",
                           "no-prebuild or no-image configs."],
         "variant": "no-prebuild | no-image"
+    },
+    {
+        "tests": ["059-finalizer-throw", "063-process-manager"],
+        "description": [ "Tests that take too long on target with gcstress and debug" ],
+        "variant": "gcstress & target & debug"
     }
 ]