[build] rename site example plugin to site-example

Just to be consistent in plugin naming convention we have today: `plugin_type-plugin_name`

So it's a `site` plugin.

plugins/pom.xml

@@ -413,7 +413,7 @@
         <module>cloud-gce</module>
         <module>cloud-azure</module>
         <module>cloud-aws</module>
-        <module>example-site</module>
+        <module>site-example</module>
         <module>lang-python</module>
         <module>lang-javascript</module>
         <module>delete-by-query</module>

plugins/site-example/pom.xml

@@ -10,7 +10,7 @@
         <version>2.0.0-beta1-SNAPSHOT</version>
     </parent>
 
-    <artifactId>elasticsearch-example-site</artifactId>
+    <artifactId>elasticsearch-site-example</artifactId>
     <name>Elasticsearch Example site plugin</name>
     <description>Demonstrates how to serve resources via elasticsearch.</description>
 

plugins/site-example/rest-api-spec/test/example/10_basic.yaml

@@ -10,6 +10,6 @@
     - do:
         nodes.info: {}
 
-    - match:  { nodes.$master.plugins.0.name: example-site  }
+    - match:  { nodes.$master.plugins.0.name: site-example  }
     - match:  { nodes.$master.plugins.0.jvm: false  }
     - match:  { nodes.$master.plugins.0.site: true  }