test/crimson: improved perf tool for crimson-msgr

New features:
* --jobs: start multiple client messengers from core #1 ~ #jobs;
* --core: can assign server core to get away from busy client cores;
* --rounds: a client will send <rounds>/<jobs> messages;

Improved:
* Better configuration report;
* Report individual client results plus a summary;
* Validate if CPU number is sufficient before running;
* Sleep 1 second while connecting, so it won't hurt performance;
* Simplify client logic and bug fixes;

Removed unecessary features:
* finish_decode() for MOSDOp;
* keepalive ratio;

Signed-off-by: Yingxin Cheng <[email protected]>