EX-2745 tests: improve hot-pools.sh to gather debug logs

EX-2745 tests: improve hot-pools.sh to gather debug logs

This patch improves hot-pools.sh to gather debug logs
for lamigo and lpurge.

Lustre-change: https://review.whamcloud.com/43111
Lustre-commit: 075ed14d944b0078fcd32ce06aa868ecaabb3adb

Test-Parameters: trivial testlist=hot-pools,hot-pools
Test-Parameters: trivial testgroup=review-dne-part-2

Change-Id: I65f23d00744499853ab099e7f097161e5e1dd66a
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/43146
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>