Prevent sleeping connections

Prevent sleeping connections in the database which get aborted
eventually. This in order to prevent growing logs.

Author: pablothedude

src/HealthCheck/DoctrineConnectionHealthCheck.php

@@ -58,11 +58,9 @@ public function check(HealthReportInterface $report)
                     $table = reset($tables);
                     // Perform a light-weight query on the chosen table
                     $query = 'SELECT * FROM `%s` LIMIT 1';
-                    $this->entityManager->getConnection()->exec(sprintf($query, $table->getName()));
+                    $this->entityManager->getConnection()->query(sprintf($query, $table->getName()));
                 }
             } catch (Exception $e) {
-                // On error close the connection to prevent sleeping processes
-                $this->entityManager->getConnection()->close();
                 return HealthReport::buildStatusDown('Unable to execute a query on the database.');
             }
         }