Init and update submodules before building

Plugins may need to refer to other existing core
Gerrit plugins and thus would need their source
code available.

Change-Id: I620276137fafaff1d02c07324ac9701a4754c09c
diff --git a/jenkins/gerrit-bazel-build-plugin-branch.sh b/jenkins/gerrit-bazel-build-plugin-branch.sh
index f8d2e06..3a49ef8 100644
--- a/jenkins/gerrit-bazel-build-plugin-branch.sh
+++ b/jenkins/gerrit-bazel-build-plugin-branch.sh
@@ -5,7 +5,8 @@
 echo "Building plugin {name}/{branch} with Gerrit/{gerrit-branch}"
 
 git remote add gerrit https://gerrit.googlesource.com/gerrit
-git fetch gerrit {gerrit-branch} && git checkout -f FETCH_HEAD
+git checkout -fb {gerrit-branch} gerrit/{gerrit-branch}
+git submodule update --init
 git read-tree -u --prefix=plugins/{name} origin/{branch}
 
 if [ -f plugins/{name}/external_plugin_deps.bzl ]
diff --git a/jenkins/gerrit-bazel-build-plugin-manual.sh b/jenkins/gerrit-bazel-build-plugin-manual.sh
index 551a9c6..6b5468d 100644
--- a/jenkins/gerrit-bazel-build-plugin-manual.sh
+++ b/jenkins/gerrit-bazel-build-plugin-manual.sh
@@ -1,6 +1,7 @@
 #!/bin/bash -e
 
-git checkout gerrit/{branch}
+git checkout -fb {branch} gerrit/{branch}
+git submodule update --init
 rm -rf plugins/{name}
 git fetch https://gerrit.googlesource.com/plugins/{name} $REFS_CHANGE
 git read-tree -u --prefix=plugins/{name} FETCH_HEAD
diff --git a/jenkins/gerrit-bazel-build-plugin.sh b/jenkins/gerrit-bazel-build-plugin.sh
index 860b5c3..573a85b 100644
--- a/jenkins/gerrit-bazel-build-plugin.sh
+++ b/jenkins/gerrit-bazel-build-plugin.sh
@@ -1,6 +1,7 @@
 #!/bin/bash -e
 
-git checkout -f gerrit/{branch}
+git checkout -fb {branch} gerrit/{branch}
+git submodule update --init
 rm -rf plugins/{name}
 git read-tree -u --prefix=plugins/{name} origin/{branch}