* Saudi Arabia, Bahrain, Oman downgraded by S&P * But investors focus instead on rising oil prices * Saudi's Jabal Omar rises on loan extension * Dubai's GFH continues climb after Abu Dhabi group buys * Egypt sluggish amid currency worries By Andrew Torchia DUBAI, Feb 18 (Reuters) - Gulf stock markets rose on Thursday amid hopes for a global deal to prop up oil prices, as investors largely ig**red sharp downgrades of the credit ratings of three nations in the region. ...