Fix grains and display

Change-Id: I7bed3b24b63ad7aa274c1adb40c7b3f0ed025462
diff --git a/_grains/jenkins_plugins.py b/_grains/jenkins_plugins.py
index 5d16d52..f5f90dc 100644
--- a/_grains/jenkins_plugins.py
+++ b/_grains/jenkins_plugins.py
@@ -13,9 +13,17 @@
 
     output = { "jenkins_plugins" : {} }
     opts = salt.config.minion_config('/etc/salt/minion')
-    user = opts['jenkins']['user']
-    password = opts['jenkins']['password']
-    url = opts['jenkins']['url']
+    try:
+        url = opts['jenkins']['url']
+    except KeyError:
+        return {}
+
+    try:
+        user = opts['jenkins']['user']
+        password = opts['jenkins']['password']
+    except KeyError:
+        user = None
+        password = None
 
     server = jenkins.Jenkins(url, username=user, password=password)
     plugins = server.get_plugins(depth=1)