webadmin: disable 'Remove' for OVF store not in ILLEGAL status

Currently when OVF store isn't in ILLEGAL status it can't be removed,
this patch greys out the remove button in the webadmin in that case.

Change-Id: Ie2defe1bc6dfb1a770546bc664bb141d0923a1fa
Bug-Url: https://bugzilla.redhat.com/1131845
Signed-off-by: Liron Aravot <laravot@redhat.com>