The change adds the option to set the default panel within horizon.
this change is useful when a tenant has many hundreds of vms and
running into horizon login slowness due to poorly crafted api
calls and sql statements.
Change-Id: If3da12a466d4953a176ec8e45499bf1cd9452ae5
Closes-Bug: #1533830
Signed-off-by: Kevin Carter <kevin.carter@rackspace.com>