DataSourceProvider: Validate connection

So far, when sending a request to the database, it was possible to try to
reuse an already closed connection which resulted in a 500 error.

Validate connections are still valid when they are borrowed and returned
to the connection pool.

Change-Id: I3376c872f6183ff7392ca2c8e354ed71a481ce0f

gerrit-server/src/main/java/com/google/gerrit/server/schema/DataSourceProvider.java

@@ -141,6 +141,8 @@ public class DataSourceProvider implements Provider<DataSource>, LifecycleListen
       long evictIdleTimeMs = 1000L * 60;
       ds.setMinEvictableIdleTimeMillis(evictIdleTimeMs);
       ds.setTimeBetweenEvictionRunsMillis(evictIdleTimeMs / 2);
+      ds.setTestOnBorrow(true);
+      ds.setTestOnReturn(true);
       ds.setValidationQuery(dst.getValidationQuery());
       ds.setValidationQueryTimeout(5);
       exportPoolMetrics(ds);