MIDEAST STOCKS-Disappointing earnings hit UAE, Egypt; Saudi soft

* Banks drag Abu Dhabi bourse down after weak quarterlies * Dubai Islamic Bank continues sliding after earnings * Egypt's OTMT posts big net loss for 2015 * Saudi rises during week on economic reforms * Qatar supported by positive earnings By Celine Aswad DUBAI, April 28 (Reuters) - Disappointing quarterly earnings among big banks pulled down stock markets in the United Arab Emirates on Thursday, while Orascom Telecom posted a big net loss that weighed on Egypt's bourse. Abu Dhabi's index lost 1