storage test: use new file for testTouchCreateFile()

this test would never succeed, because the previous test -
testFOpen() - creates the file 'foo', but testTouchCreateFile()
starts out by asserting it doesn't exist. Change the test to
use a file called 'touch' instead (which does not previously
exist).

tests/lib/files/storage/storage.php

@@ -340,10 +340,10 @@ abstract class Storage extends \PHPUnit_Framework_TestCase {
 	}
 
 	public function testTouchCreateFile() {
-		$this->assertFalse($this->instance->file_exists('foo'));
+		$this->assertFalse($this->instance->file_exists('touch'));
 		// returns true on success
-		$this->assertTrue($this->instance->touch('foo'));
-		$this->assertTrue($this->instance->file_exists('foo'));
+		$this->assertTrue($this->instance->touch('touch'));
+		$this->assertTrue($this->instance->file_exists('touch'));
 	}
 
 	public function testRecursiveRmdir() {