ElasticReindexIT: Increase -Xmx to 1024m to fix test

For Java 8 the test fails with 512 MB of maximum heap size and takes
*really* long. Increasing this value to 1024 MB passes the test for me.

Bug: Issue 11543
Change-Id: Ie8e17770ddfebda569a8151e1b630f5a4e865c7b
diff --git a/javatests/com/google/gerrit/acceptance/pgm/BUILD b/javatests/com/google/gerrit/acceptance/pgm/BUILD
index d15c6ce..57b93f6 100644
--- a/javatests/com/google/gerrit/acceptance/pgm/BUILD
+++ b/javatests/com/google/gerrit/acceptance/pgm/BUILD
@@ -30,7 +30,7 @@
         "pgm",
         "no_windows",
     ],
-    vm_args = ["-Xmx512m"],
+    vm_args = ["-Xmx1024m"],
     deps = [
         ":util",
         "//java/com/google/gerrit/elasticsearch",