MDL-55986 behat: Added option to optimize parallel runs by tags

run.php should only be used for running behat
before this patch if tags were passed, then behat.yml
was being re-written with features havings tags.
As this is not ideal, this option is now removed and
features with tags will be optimally split
by init.php when --optimize-run option is passed

lib/behat/classes/util.php

@@ -216,12 +216,13 @@ class behat_util extends testing_util {
      * Stores a file in dataroot/behat to allow Moodle to switch
      * to the test environment when using cli-server.
      * @param bool $themesuitewithallfeatures if only theme specific features need to be included in the suite.
+     * @param string $tags comma separated tag, which will be given preference while distributing features in parallel run.
      * @param int $parallelruns number of parallel runs.
      * @param int $run current run.
      * @throws coding_exception
      * @return void
      */
-    public static function start_test_mode($themesuitewithallfeatures = false, $parallelruns = 0, $run = 0) {
+    public static function start_test_mode($themesuitewithallfeatures = false, $tags = '', $parallelruns = 0, $run = 0) {
         global $CFG;
 
         if (!defined('BEHAT_UTIL')) {
@@ -237,7 +238,7 @@ class behat_util extends testing_util {
         self::test_environment_problem();
 
         // Updates all the Moodle features and steps definitions.
-        behat_config_manager::update_config_file('', true, '', $themesuitewithallfeatures, $parallelruns, $run);
+        behat_config_manager::update_config_file('', true, $tags, $themesuitewithallfeatures, $parallelruns, $run);
 
         if (self::is_test_mode_enabled()) {
             return;