WASHINGTON, Tuesday, Aug. 11. A private letter received here to-day from a prominent officer at Warrenton, says that a rebel Lieutenant, who deserted from their army and came into our lines last Sunday, reports that great dissatisfaction exists among the North Carolina, Tennessee and Mississippi troops, particularly among the former, at the condition of affairs in their respective States. The North Carolina troops threaten to mutiny unless they are sent back to their homes. Once there, they say they will throw down their arms, and abandon the rebel cause, of which they are heartily sick. It is only with great...