pgbench: If we fail to send a command to the server, fail.

This beats the old behavior of busy-waiting hands down.

Oversight in commit 12788ae4.

Report by Pavan Deolasee. Patch by Fabien Coelho.  Reviewed by
Pavan Deolasee.

Discussion: http://postgr.es/m/CABOikdPhfXTypckMC1Ux6Ko+hKBWwUBA=EXsvamXYSg8M9J94w@mail.gmail.com

src/bin/pgbench/pgbench.c

@@ -2194,12 +2194,8 @@ doCustom(TState *thread, CState *st, StatsData *agg)
 				{
 					if (!sendCommand(st, command))
 					{
-						/*
-						 * Failed. Stay in CSTATE_START_COMMAND state, to
-						 * retry. ??? What the point or retrying? Should
-						 * rather abort?
-						 */
-						return;
+						commandFailed(st, "SQL command send failed");
+						st->state = CSTATE_ABORTED;
 					}
 					else
 						st->state = CSTATE_WAIT_RESULT;