Propagate IOException when reading refs.

Currently, Repository.getAllRefs() and Repository.getTags() silently
ignores an IOException and instead returns an empty map. Repository
is a public API in JGit and as such cannot be changed until the next
major revision change. Until then, update all call sites to use the
RefDatabase directly, since it propagates the error.

Change-Id: Ia3894a40fbc99482cbb4e1d6b3e4b69e5ddacba2

gerrit-server/src/main/java/com/google/gerrit/server/schema/Schema_56.java

@@ -24,6 +24,7 @@ import com.google.inject.Provider;
 import org.eclipse.jgit.errors.RepositoryNotFoundException;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.RefDatabase;
 import org.eclipse.jgit.lib.RefUpdate;
 import org.eclipse.jgit.lib.Repository;
 
@@ -61,7 +62,15 @@ public class Schema_56 extends SchemaVersion {
         continue;
       }
       try {
-        Map<String, Ref> all = git.getAllRefs();
+        Map<String, Ref> all;
+        try {
+          all = git.getRefDatabase().getRefs(RefDatabase.ALL);
+        } catch (IOException e) {
+          ui.message("warning: " + name.get() + ": Cannot read refs: "
+              + e.getMessage());
+          e.printStackTrace();
+          continue;
+        }
         if (all.keySet().equals(keysOne) || all.keySet().equals(keysTwo)) {
           try {
             RefUpdate update = git.updateRef(Constants.HEAD);