Add "target_suffix" to gerrit_plugin()

Updating gerrit_plugin.bucklet to match default.defs for Gerrit.

The "target_suffix" parameter is added to the gerrit_plugin()
definition as a way to facilitate a custom "post-build" type of
step, such as with the Gitiles plugin, where the additional static
files need to be moved into the root of the JAR file.

Change-Id: I4e855bdcbb2a2705687e52d3287b7bc8e253391a
diff --git a/gerrit_plugin.bucklet b/gerrit_plugin.bucklet
index d4edb7f..4b8f418 100644
--- a/gerrit_plugin.bucklet
+++ b/gerrit_plugin.bucklet
@@ -72,7 +72,8 @@
     gwt_module = None,
     manifest_entries = [],
     type = 'plugin',
-    visibility = ['PUBLIC']):
+    visibility = ['PUBLIC'],
+    target_suffix = ''):
   from multiprocessing import cpu_count
   from os import path,getcwd
   # TODO(davido): Remove this hack and replace all this mess with just
@@ -150,7 +151,7 @@
     )
 
   java_binary(
-    name = name,
+    name = name + target_suffix,
     manifest_file = ':%s__manifest' % name,
     merge_manifests = False,
     deps = [