Remove unnecessary manifest creation in config_install_default_config()

Here's a patch that adds a test to ensure manifests are written for config entities and removes the unnecessary code - which was made unnecessary due to #1806178: Remove code duplication for hook_config_import_*() implementations of config entities.

New patch that ensures an empty manifest is created for each config entity whether or not a default config entity is provided. Tests added for this too.

Actually we want to create empty manifest files even if the module has no config directory!

#4: 1889752.4.drupal8.manifest.patch queued for re-testing.

Got a fatal php error in testRegression_310447() - nought to do with this change - so requested retest.

oh wow! the fatal is caused by this patch ...

exception 'PDOException' with message 'SQLSTATE[42S02]: Base table or view not found: 1146 Table 'drupal8alt.simpletest694268node_type' doesn't exist' in /Users/alex/dev/sites/drupal8alt.dev/core/lib/Drupal/Core/Database/Statement.php:58
Stack trace:
#0 /Users/alex/dev/sites/drupal8alt.dev/core/lib/Drupal/Core/Database/Statement.php(58): PDOStatement->execute(Array)
#1 /Users/alex/dev/sites/drupal8alt.dev/core/lib/Drupal/Core/Database/Connection.php(523): Drupal\Core\Database\Statement->execute(Array, Array)
#2 /Users/alex/dev/sites/drupal8alt.dev/core/lib/Drupal/Core/Database/Query/Select.php(421): Drupal\Core\Database\Connection->query('SELECT nt.*?FRO...', Array, Array)
#3 /Users/alex/dev/sites/drupal8alt.dev/core/modules/node/node.module(725): Drupal\Core\Database\Query\Select->execute()
#4 /Users/alex/dev/sites/drupal8alt.dev/core/modules/node/node.module(370): _node_types_build()
#5 /Users/alex/dev/sites/drupal8alt.dev/core/modules/node/node.module(202): node_type_get_names()
#6 /Users/alex/dev/sites/drupal8alt.dev/core/lib/Drupal/Core/Plugin/Discovery/InfoHookDecorator.php(59): node_entity_info(Array)
#7 /Users/alex/dev/sites/drupal8alt.dev/core/lib/Drupal/Component/Plugin/Discovery/ProcessDecorator.php(63): Drupal\Core\Plugin\Discovery\InfoHookDecorator->getDefinitions()
#8 /Users/alex/dev/sites/drupal8alt.dev/core/lib/Drupal/Core/Plugin/Discovery/AlterDecorator.php(58): Drupal\Component\Plugin\Discovery\ProcessDecorator->getDefinitions()
#9 /Users/alex/dev/sites/drupal8alt.dev/core/lib/Drupal/Component/Plugin/PluginManagerBase.php(59): Drupal\Core\Plugin\Discovery\AlterDecorator->getDefinitions()
#10 /Users/alex/dev/sites/drupal8alt.dev/core/lib/Drupal/Core/Entity/EntityManager.php(264): Drupal\Component\Plugin\PluginManagerBase->getDefinitions()
#11 /Users/alex/dev/sites/drupal8alt.dev/core/includes/entity.inc(36): Drupal\Core\Entity\EntityManager->getDefinitions()
#12 /Users/alex/dev/sites/drupal8alt.dev/core/includes/config.inc(292): entity_get_info()
#13 /Users/alex/dev/sites/drupal8alt.dev/core/includes/config.inc(29): config_get_module_config_entities('database_test')
#14 /Users/alex/dev/sites/drupal8alt.dev/core/includes/module.inc(549): config_install_default_config('module', 'database_test')
#15 /Users/alex/dev/sites/drupal8alt.dev/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php(223): module_enable(Array, false)
#16 /Users/alex/dev/sites/drupal8alt.dev/core/modules/system/lib/Drupal/system/Tests/Database/DatabaseTestBase.php(22): Drupal\simpletest\DrupalUnitTestBase->enableModules(Array)
#17 /Users/alex/dev/sites/drupal8alt.dev/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php(702): Drupal\system\Tests\Database\DatabaseTestBase->setUp()
#18 /Users/alex/dev/sites/drupal8alt.dev/core/scripts/run-tests.sh(381): Drupal\simpletest\TestBase->run()
#19 /Users/alex/dev/sites/drupal8alt.dev/core/scripts/run-tests.sh(22): simpletest_script_run_one_test('17', 'Drupal\system\T...')
#20 {main}

So when installing the 'database_test' module simpletest thinks it's got node installed but actually it hasn't... funnily enough this test does not even need node installed.

#9: 1889752.9.drupal8.manifest.patch queued for re-testing.