webadmin: Fix Unlimited quota is counted as -1

In the quota main tab, when using specific quota which includes at least
one unlimited cluster/storage-domain, the unlimited quota is counted as
-1 (the int value of the constant).

Fixed calculation to ignore both the consumption and the allocation of
unlimited quota.

Change-Id: I7f49bfe3576cecccf80e9ad2105506e3eb267d83
Bug-Url: https://bugzilla.redhat.com/919088
Signed-off-by: Ofri Masad <omasad@redhat.com>