Use bazelisk for gerrit and plugins builds

Bazelisk allows to automatically switch between bazel versions
using the .bazelversion file on the Gerrit home folder.

Change-Id: Ie1bdae2a2f350e900cb666b8e5b8d0ee42c15a4a

jenkins/gerrit-bazel-build-plugin.sh

diff --git a/jenkins/gerrit-bazel-build-plugin.sh b/jenkins/gerrit-bazel-build-plugin.sh
index 9cb9bc7..860b5c3 100644
--- a/jenkins/gerrit-bazel-build-plugin.sh
+++ b/jenkins/gerrit-bazel-build-plugin.sh
@@ -14,11 +14,12 @@
 
 . set-java.sh 8
 
-bazel build --spawn_strategy=standalone --genrule_strategy=standalone $TARGETS
+bazelisk version
+bazelisk build --spawn_strategy=standalone --genrule_strategy=standalone $TARGETS
 
 if [ "$TEST_TARGET" != "" ]
 then
-    bazel test --test_env DOCKER_HOST=$DOCKER_HOST plugins/{name}:$TEST_TARGET
+    bazelisk test --test_env DOCKER_HOST=$DOCKER_HOST plugins/{name}:$TEST_TARGET
 fi
 
 for JAR in $(find bazel-bin/plugins/{name} -name {name}*.jar)