Implement and use factory for BackendException

* VuFindSearch/Backend/Solr/Connector.php (send): Use exception
  factory.
* VuFindSearch/Backend/Exception/BackendException.php
  (createFromResponse): New function. Create exception based on
  server response.

module/VuFindSearch/src/VuFindSearch/Backend/Exception/BackendException.php

@@ -60,6 +60,27 @@ class BackendException extends RuntimeException
      */
     protected $response;
 
+    /**
+     * Exception factory.
+     *
+     * Returns a RequestErrorException or RemoteErrorException depending on
+     * the response's status code.
+     *
+     * @param Response $response Server response
+     *
+     * @return RequestErrorException|RemoteErrorException
+     */
+    public static function createFromResponse(Response $response)
+    {
+        $status = $response->getStatusCode();
+        $phrase = $response->getReasonPhrase();
+        if ($status >= 500) {
+            return new RemoteErrorException($phrase, $status, $response);
+        } else {
+            return new RequestErrorException($phrase, $status, $response);
+        }
+    }
+
     /**
      * Constructor.
      *

module/VuFindSearch/src/VuFindSearch/Backend/Solr/Connector.php

@@ -37,9 +37,7 @@ use VuFindSearch\Query\Query;
 
 use VuFindSearch\ParamBag;
 
-use VuFindSearch\Backend\Exception\RemoteErrorException;
-use VuFindSearch\Backend\Exception\RequestErrorException;
-use VuFindSearch\Backend\Exception\RequestParseErrorException;
+use VuFindSearch\Backend\Exception\BackendException;
 
 use VuFindSearch\Backend\Solr\Document\AbstractDocument;
 
@@ -405,13 +403,7 @@ class Connector
         }
 
         if (!$response->isSuccess()) {
-            $status = $response->getStatusCode();
-            $phrase = $response->getReasonPhrase();
-            if ($status >= 500) {
-                throw new RemoteErrorException($phrase, $status, $response);
-            } else {
-                throw new RequestErrorException($phrase, $status, $response);
-            }
+            throw BackendException::createFromResponse($response);
         }
         return $response->getBody();
     }