Use patch instead of sed to update Gerrit's x/ route

We modify the x/ route to ensure we can serve git repos from x/.
Previously we had been using sed which is likely to be much more fragile
than patch. Patch will detect conflicts and other errors which would be
good for us to find out about early.

Change-Id: Ic324c7777e7851a6150e4415338c4628ac710970

docker/gerrit/patches/serve-x-normally.patch

@@ -0,0 +1,13 @@
+diff --git a/java/com/google/gerrit/httpd/raw/StaticModule.java b/java/com/google/gerrit/httpd/raw/StaticModule.java
+index 414a120194..9d59535a66 100644
+--- a/java/com/google/gerrit/httpd/raw/StaticModule.java
++++ b/java/com/google/gerrit/httpd/raw/StaticModule.java
+@@ -71,7 +71,7 @@ public class StaticModule extends ServletModule {
+           "/c/*",
+           "/p/*",
+           "/q/*",
+-          "/x/*",
++          //"/x/*",
+           "/admin/*",
+           "/dashboard/*",
+           "/groups/self",

playbooks/zuul/gerrit/run.yaml

@@ -2,9 +2,12 @@
   tasks:
     - name: Patch Gerrit's webapp routes to not shadow x/
       shell: |
-        cd /home/zuul/src/gerrit.googlesource.com/gerrit
+        set -ex
+        GERRIT_BASE=/home/zuul/src/gerrit.googlesource.com/gerrit
+        SYSTEM_CONFIG_BASE=/home/zuul/src/opendev.org/opendev/system-config
         # Disable the x/ redirection since we have x/ projects
-        sed -i -e 's|"/x/\*"\,$|//"/x/*",|g' java/com/google/gerrit/httpd/raw/StaticModule.java
+        patch $GERRIT_BASE/java/com/google/gerrit/httpd/raw/StaticModule.java \
+          $SYSTEM_CONFIG_BASE/docker/gerrit/patches/serve-x-normally.patch
 
     - name: Build gerrit
       include_role: