Shorten sleep for racy run-test 063.

Didn't look closely enough to know exactly why this needs to be
shortened, but I've verified that it fixes the case where we run with:
--interpreter, --optimizing, and --gcstress.

Bug: 2310700
Test: ./art/test/testrunner/run_build_test_target.py -j110
art-read-barrier-gcstress

Change-Id: Ic82f1bbb178c0debdfafc260084e760df226e298
diff --git a/test/063-process-manager/src/Main.java b/test/063-process-manager/src/Main.java
index 311c4e7..e31a0df 100644
--- a/test/063-process-manager/src/Main.java
+++ b/test/063-process-manager/src/Main.java
@@ -16,7 +16,7 @@
         System.out.println("spawning child");
         ProcessBuilder pb = new ProcessBuilder("sleep", "5");
         Process proc = pb.start();
-        Thread.sleep(2000);
+        Thread.sleep(250);
         checkManager();
         proc.waitFor();
         System.out.println("child died");