(Reuters) - Hewlett-Packard Co announced the launch of a $169 tablet powered by the Android operating system, a centerpiece of the company's effort to expand in mobile devices and reduce its dependence on the shrinking personal computer market. The launch of the Slate 7 marks HP's latest foray into the consumer tablet market. It follows the 2011 failure of its WebOS-based TouchPad, which the company stopped selling after just seven weeks, citing poor demand. Powered by Android 4. ...