[WAGON-449] Use new connection manager when set

Recreate the http-wagon CLIENT after calling
setPoolingHttpClientConnectionManager.

This also includes setting CLIENT to a nonfinal field, and as a result
its name is changed to httpClient to satisfy naming conventions.

pom.xml

@@ -128,6 +128,9 @@ under the License.
     <contributor>
       <name>Grzegorz Grzybek</name>
     </contributor>
+    <contributor>
+      <name>Jean Niklas L'orange</name>
+    </contributor>
   </contributors>
 
   <mailingLists>

wagon-providers/wagon-http/src/main/java/org/apache/maven/wagon/providers/http/AbstractHttpClientWagon.java

@@ -364,7 +364,7 @@ private static PoolingHttpClientConnectionManager createConnManager()
         return connManager;
     }
 
-    private static final CloseableHttpClient CLIENT = createClient();
+    private static CloseableHttpClient httpClient = createClient();
 
     private static CloseableHttpClient createClient()
     {
@@ -481,6 +481,7 @@ public static void setPoolingHttpClientConnectionManager(
         PoolingHttpClientConnectionManager poolingHttpClientConnectionManager )
     {
         httpClientConnectionManager = poolingHttpClientConnectionManager;
+        httpClient = createClient();
     }
 
     public void put( File source, String resourceName )
@@ -829,7 +830,7 @@ protected CloseableHttpResponse execute( HttpUriRequest httpMethod )
             }
         }
 
-        return CLIENT.execute( httpMethod, localContext );
+        return httpClient.execute( httpMethod, localContext );
     }
 
     protected void setHeaders( HttpUriRequest method )