server.tests: Fix an indent problem in control of multihost_migration

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
server.tests: Update the hostid in multihost_migration from machines to ips

As hostid is used to compared with hosts in parameter to judge if the
host is src host for migration. The hostid should use the same type
of parameter with hosts. Otherwise, it lead to a failed to get the right
src host in test script.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>