After giving a nearly six-month tryout for the Internet talk show host Cenk Uygur, the cable news channel MSNBC is preparing to instead hand its 6 p.m. time slot to the Rev. Al Sharpton. Mr. Sharpton’s imminent hiring, which was acknowledged by three people at the channel on condition of anonymity because the contract had not been signed, is significant in part because MSNBC and other news channels have been criticized for a paucity of minority hosts in prominent time slots. Mr. Sharpton, who is black and is a well-known civil rights activist and radio host, has been guest hosting...