MDL-55548 backup: changes after review

1) There is no need to store the 'timemodified' value of
the section when backing up a course module, they do
not refer to the same time.
2) When creating a new course section during restore use
the current time.
3) Added timemodified value to more places when updating
the 'course_sections' table.

availability/classes/info_section.php

@@ -62,8 +62,12 @@ class info_section extends info {
 
     protected function set_in_database($availability) {
         global $DB;
-        $DB->set_field('course_sections', 'availability', $availability,
-                array('id' => $this->section->id));
+
+        $section = new \stdClass();
+        $section->id = $this->section->id;
+        $section->availability = $availability;
+        $section->timemodified = time();
+        $DB->update_record('course_sections', $section);
     }
 
     /**