XStyleLoader2 : enhance unit test to PageStyle

and remove duplicate code

Change-Id: Ib9e3568c860fe5cd3f11374a1c61dff101e33a18
Reviewed-on: https://gerrit.libreoffice.org/10832
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>