Fix FieldAttachTestCase::setUp() signature

From #520106-132: Allow setting the active menu trail for dynamically-generated menu paths., apparently classes which inherit from DrupalWebTestCase need to have the following function signature for setUp:

function setUp() {
  // ...
}

In FieldAttachTestCase, the signature is

function setUp($modules = array()) {
  // ...
}

which apparently can raise an E_STRICT warning.

Instead we should use something like

function setUp() {
  $modules = func_get_args();
  if (isset($modules[0]) && is_array($modules[0])) {
    $modules = $modules[0];
  }
  // ...