This commit changes the WC_Tests_Product_CSV_Importer class to use artificial HTTP responses instead of performing real HTTP requests to a external server to get the images of the imported products. On my local machine, this change reduced the test execution time from 3257ms to 831ms.
As a consequence of this change, this commit also fixes WC_Tests_Product_CSV_Importer::test_import() in all Travis builds. This test has been failing for a few weeks on Travis but not on our local environments. After some debugging, I found out that the test was failing on Travis because of the following error when `wp_safe_remote_get()` was called to get images for the imported products:
```
Error getting remote image http://demo.woothemes.com/woocommerce/wp-content/uploads/sites/56/2013/06/T_1_front.jpg. Error: cURL error 35: gnutls_handshake() failed: Handshake failed.
```
Apparently, the PHP binary that is used by Travis is unable to handle the TLS handshake (see https://github.com/travis-ci/travis-ci/issues/6339) and the test probably started failing when demo.woothemes.com (which is used to download the images for the imported products) switched from HTTP to HTTPS.
[According to the WooCommerce wiki](https://github.com/woocommerce/woocommerce/wiki/Order-and-Order-Line-Item-Data) and `WC_REST_Orders_Controller`, WooCommerce stores country codes using the ISO 3166-1 alpha-2 (2 character) standard. However, the `WC_Tests_Order_Functions::test_wc_get_order_address_params()` test method was using 'USA' instead of 'US'.
As @claudiosanches pointed out, there isn't much real-world need for `WC_Install::get_tables()` to sort results. Instead, sort the returned value within the `WC_Tests_Install::test_get_tables()` method.
Since custom tables can be registered within WooCommerce via the 'woocommerce_install_get_tables' filter, it's helpful to ensure that `WC_Install::get_tables()` automatically sorts the table names alphabetically.
This helps avoid false failures when testing a plugin that uses a custom table against the WooCommerce core test suite, as queries like `WC_Tests_Install::test_get_tables()` assumes that tables will be returned in alphabetical order.