Propagate errors to top-level for TPCC

[danielmitterdorfer]

With this commit we propagate all errors in any of the TPCC subcommands to the top-level and exit the application with an error message and a non-zero exit code.

Closes #206

[pingcap-cla-assistant]

All committers have signed the CLA.

[danielmitterdorfer]

A couple of notes on the implementation:

When we test the scenario from #206 now, we get the following behavior:

begin to check warehouse 1 at condition 3.3.2.9
begin to check warehouse 1 at condition 3.3.2.10
Error: check warehouse 1 at condition 3.3.2.10 failed exec SELECT count(*)
        FROM (  SELECT  c.c_id, c.c_d_id, c.c_w_id, c.c_balance c1,
                                   (SELECT sum(ol_amount) FROM orders, order_line
                                         WHERE OL_W_ID=O_W_ID
                                           AND OL_D_ID = O_D_ID
                                           AND OL_O_ID = O_ID
                                           AND OL_DELIVERY_D IS NOT NULL
                                           AND O_W_ID=?
                                           AND O_D_ID=c.C_D_ID
                                           AND O_C_ID=c.C_ID) sm, (SELECT  sum(h_amount)  from  history
                                                                                                WHERE H_C_W_ID=?
                                                                                                  AND H_C_D_ID=c.C_D_ID
                                                                                                  AND H_C_ID=c.C_ID) smh
                         FROM customer c
                        WHERE  c.c_w_id = ? ) t
   WHERE c1<>sm-smh failed driver: bad connection

$ echo $?
1

I also added cmd.SilenceUsage = true to all subcommands (but not the root command) to suppress that an additional usage string is shown after the error message (which is cobra's default behavior).