webadmin : Fix for rebalance status popup not coming up

Fix for rebalance status popup not coming up.
The issue was with date parser getting an empty string
not being handled appropriately.

Change-Id: I9087a10c7d71a7cfca3af23916062cdc92f4198f
Signed-off-by: Anmol Babu <anbabu@redhat.com>