[autotest] WMatrix link on AFE.

RPC get_static_data will get wmatrix_url from config file and send to frontend.
If wmatrix_url is not present or set to empty, the WMatrix link will not show
up on AFE. Otherwise, it will on the top-right corner.

BUG=chromium:391851
TEST=edit config files, ran afe
DEPLOY=afe,apache

Change-Id: I29948ec59d203ac84d60e68d2c5a9b612b9a4cbc
Reviewed-on: https://chromium-review.googlesource.com/206896
Tested-by: Jiaxi Luo <jiaxiluo@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
Commit-Queue: Jiaxi Luo <jiaxiluo@chromium.org>
diff --git a/frontend/afe/rpc_interface.py b/frontend/afe/rpc_interface.py
index bd68425..879a148 100644
--- a/frontend/afe/rpc_interface.py
+++ b/frontend/afe/rpc_interface.py
@@ -975,6 +975,9 @@
                                    "Waiting": "Waiting for scheduler action",
                                    "Archiving": "Archiving results",
                                    "Resetting": "Resetting hosts"}
+
+    result['wmatrix_url'] = rpc_utils.get_wmatrix_url()
+
     return result