EX-2718 tests: remove lpurge mds validation

EX-2718 tests: remove lpurge mds validation

The lpurge changes for EX-2718 (use local mountpoint
for purge operations) lands with commit dfa0760e7d8.
However, the hot-pools.sh changes were missing somehow.
This patch adds the changes back to remove lpurge
mds validation.

Lustre-change: https://review.whamcloud.com/43140
Lustre-commit: 7b00329e09ef73335e33dd8e83bb7993c39990e9

Fixes: dfa0760e7d8 ("EX-2718 lpurge: use local mountpoint for purge operations")
Change-Id: I55a40dfd958e40859ddb5e98b3f76ad568d0095b
Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/43528
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>