Add new socket mode DISCONNECT_AFTER_READING_REQUEST Useful for writing tests related to POST requests with retryable and unretryable bodies. (cherry picked from 3088bcc1d22f3e163e5e7ecbc997daadfdaaeec3) bug: 10211309 Change-Id: Icb042d5875c4651348103be4eed7a2e248449b52