The Docker-based local environment should install the WordPress Importer plugin

[johnbillion]

Setting up the Docker-based local environment on a fresh installation and running the tests results in failures due to the missing WordPress Importer plugin.

The npm run env:install command should also install the appropriate version of the WordPress Importer plugin in the local environment.

Failures:

1) Tests_Import_Import::test_small_import
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/import.php:23

2) Tests_Import_Import::test_double_import
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/import.php:23

3) Tests_Import_Import::test_ordering_of_importers
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/import.php:23

4) Tests_Import_Import::test_slashes_should_not_be_stripped
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/import.php:23

5) Tests_Import_Parser::test_malformed_wxr
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/parser.php:21

6) Tests_Import_Parser::test_invalid_wxr
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/parser.php:21

7) Tests_Import_Parser::test_wxr_version_1_1
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/parser.php:21

8) Tests_Import_Parser::test_wxr_version_1_0
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/parser.php:21

9) Tests_Import_Parser::test_escaped_cdata_closing_sequence
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/parser.php:21

10) Tests_Import_Parser::test_unescaped_cdata_closing_sequence
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/parser.php:21

11) Tests_Import_Postmeta::test_serialized_postmeta_no_cdata
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/postmeta.php:21

12) Tests_Import_Postmeta::test_utw_postmeta
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/postmeta.php:21

13) Tests_Import_Postmeta::test_serialized_postmeta_with_cdata
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/postmeta.php:21

14) Tests_Import_Postmeta::test_serialized_postmeta_with_evil_stuff_in_cdata
This test requires the WordPress Importer plugin to be installed in the test suite. See: https://make.wordpress.org/core/handbook/contribute/git/#unit-tests

/var/www/tests/phpunit/tests/import/postmeta.php:21