EX-5824 test: hot-pools test_57: data copy failed: mirror failed

EX-5824 test: hot-pools test_57: data copy failed: mirror failed

Add debug prints in hot-pools test_57

Test-Parameters: trivial env=FAIL_ON_ERROR=false,ONLY=56-57 testlist=hot-pools

Change-Id: I863b580f5483c14c24c6f79ebdddbc782b65e945
Signed-off-by: Alexandre Ioffe <aioffe@ddn.com>
Reviewed-on: https://review.whamcloud.com/48477
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>