logger: rename and change a role of select_log_formatter()

This patch renames select_log_formatter(). The new name is
early_log_init().

early_log_init() is also used for selecting log formatter, but it
also used for registering information of logger user. The information
is registered as 2nd parameter of the function which is typed struct
logger_user_info.

Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
logger: expand MAX_MSG_SIZE

JSON formatter produces long line in logs, so 256 is not enough for
MAX_MSG_SIZE.

Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
test: support log format select with $LOG_FORMAT

Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
test: collect logs of sheeps after tests

After completion of tests, sheep.log of sheeps are collected in a
directory whose name is "logs.`date +%Y-%m-%d-%H-%M-%S`".

Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
script: json_log_viewer.py for collecting and viewing multiple log files of sheeps

This patch adds a new script: json_log_viewer.py for collecting and
viewing multiple log files of sheeps.

This script is useful for reading log files produced during running
test scripts. Because test scripts execute every sheep process on one
machine, sorting their log entries with timestamp is meaningful.

Simple description of usage and screenshot is here:
http://github.com/mitake/sheepdog/wiki/json_log_viewer.py

Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>