Don't use a prepared statement for the active build steps query

Prepared statements are sometimes much slower than unprepared
statements, because the planner doesn't have access to the query
parameters.  This is the case for the active build steps query (in
/status), where a prepared statement is three orders of magnitude
slower.  So disable the use of prepared statements in this case.

(Since the query parameters are constant here, it would be nicer if we
could tell DBIx::Class to prepare a statement with those parameters
fixed.  But I don't know an easy way to do so.)

src/lib/Hydra/Controller/Root.pm

@@ -95,11 +95,15 @@ sub timeline :Local {
 
 sub status :Local {
     my ($self, $c) = @_;
-    $c->stash->{steps} = [ $c->model('DB::BuildSteps')->search(
-        { 'me.busy' => 1, 'build.busy' => 1 },
-        { join => [ 'build' ]
-        , order_by => [ 'machine' ]
-        } ) ];
+    $c->model('DB')->storage->dbh_do(sub {
+        my (undef, $dbh) = @_;
+        local $dbh->{pg_server_prepare} = 0;
+        $c->stash->{steps} = [ $c->model('DB::BuildSteps')->search(
+            { 'me.busy' => 1, 'build.finished' => 0, 'build.busy' => 1 },
+            { join => [ 'build' ]
+            , order_by => [ 'machine' ]
+            } ) ];
+    });
 }