webadmin: Data storage domain does not always activate when created

When importing an ISO storage domain without the activation flag and then
immediately creating a data storage domain, the data storage domain is
added in maintenance mode

Bug-Url: https://bugzilla.redhat.com/1116572
Change-Id: I70eaabbfd1453276219c0e0f8f0cbf4ca5df1a55
Signed-off-by: Tal Nisan <tnisan@redhat.com>