Increase the memory used in acceptance tests

The acceptance tests are getting longer and therefore
more memory is needed because of the accumulation of Gerrit
servers heap in the JVM across tests.

Change-Id: I128b01b30348b1d93c0cd3bf081882c886702b2c

BUILD

diff --git a/BUILD b/BUILD
index 1f813d4..dc34ede 100644
--- a/BUILD
+++ b/BUILD
@@ -52,6 +52,7 @@
     srcs = glob(["src/test/java/**/*IT.java"]),
     group = "server_cache",
     labels = ["server"],
+    vm_args = ["-Xmx4g"],
     deps = [
         ":cache-chroniclemap__plugin",
         ":chroniclemap-test-lib",