EX-4865 lipe: add timestamps to lamigo and lpurge log messages

EX-4865 lipe: add timestamps to lamigo and lpurge log messages

Added optional timestamp to log messages; Added command line
option --timestamps to lamigo/lpurge and 'timestamps' keyword
to lpurge config. Added timestamps to log files to
hot-pools test frame by default.

Test-Parameters: trivial testlist=hot-pools
Signed-off-by: Alexandre Ioffe <aioffe@ddn.com>
Change-Id: If58f20eed31c6df30a70f0cb1c93430040f8fe62
Reviewed-on: https://review.whamcloud.com/46599
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>