GM aims to build 500,000 electric-technology vehicles a year

* Target would be more than 5 pct of 2011 sales total * GM has sold more than 50,000 electrified vehicles in 2012 * Goal includes gasoline engines with "eAssist" By Ben Klayman SAN FRANCISCO, Nov 14 (Reuters) - General Motors Co aims by 2017 to buld up to 500,000 vehicles a year that include some form of electric power in the engine, including cars like the Chevrolet Volt plug-in hybrid, a top executive said on Wednesday. GM has made rolling out cars with electrical technology -- including its eAssist system that boosts fuel efficiency in gasoline-powered cars -- a central part of its global strategy, global product development chief Mary Barra told reporters. "Our plans call for producing...