webadmin: Show migrating VM on destination host

Show a migrating VM both on the source host (status Migrating From)
as well as on the destination host (Migrating To).

Change-Id: Iae8228e4a6e9e7e91b8224f0ef2764c5e4e25cfa
Bug-Url: https://bugzilla.redhat.com/881593
Signed-off-by: Libor Spevak <lspevak@redhat.com>