Isolate globals for ContentSecurityPolicy tests

Isolate globals for ContentSecurityPolicy tests

With "$wgResourceBasePath = '/';", various ContentSecurityPolicy tests
failed due to unexpected output. An extra "extensions" is added in the
output line.

The reason is getAdditionalSelfUrls() injecting URls from a few global
settings but the test fails to set them in setUp(). The settings are:

  $wgLoadScript
  $wgExtensionAssetsPath
  $wgStylePath
  $wgResourceBasePath

Set them explicitly in setUp() so the test outcome does not depend on
values that might have been set in LocalSettings.php.

Add a quick test to ensure getAdditionalSelfUrls() does recognize
domains in those four global settings.

Change-Id: Ia0dc2f44c71bdf89a0ee9ef82d9cb6a1cbd8a9da