tpcc: add wait times on each transactions

[mahjonp]

Add Keying Time and Thinking Time between txn execution and two flags.

Usage:
  go-tpc tpcc run [flags]

Flags:
  -h, --help   help for run
      --wait   including keying & thinking time described on TPC-C Standard Specification

For example.

./bin/go-tpc tpcc --warehouses 4 run --wait

[siddontang]

I can't understand keying and thinking easily, can you use other words or refer to other TPCC implementation at first then think a better name?

[coocood]

LGTM

[mahjonp]

I can't understand keying and thinking easily, can you use other words or refer to other TPCC implementation at first then think a better name?

I combined them into one wait flag.

[zhouqiang-cl]

LGTM