Fix delete user acceptance test

Adding some missing asserts showed that the "delete user" acceptance
test was silently failing, as the deletion was not being confirmed in
the dialog and thus the user was not being deleted.

The dialog button contains a single quote ("user0's"), so the XPath
expression had to be adjusted (it seems that it is not possible to
escape a single quote in a string enclosed in single quotes in XPath
1.0).

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>

tests/acceptance/features/bootstrap/DialogContext.php

@@ -38,7 +38,7 @@ class DialogContext implements Context, ActorAwareInterface {
 	 * @return Locator
 	 */
 	public static function theDialogButton($text) {
-		return Locator::forThe()->xpath("//button[normalize-space() = '$text']")->
+		return Locator::forThe()->xpath("//button[normalize-space() = \"$text\"]")->
 			descendantOf(self::theDialog())->
 			describedAs($text . " button of the dialog");
 	}

tests/acceptance/features/users.feature

@@ -30,6 +30,7 @@ Feature: users
     And I open the actions menu for the user user0
     And I see that the "Delete user" action in the user0 actions menu is shown
     When I click the "Delete user" action in the user0 actions menu
+    And I click the "Delete user0's account" button of the confirmation dialog
     Then I see that the list of users does not contains the user user0
 
   Scenario: disable a user