I get it running now. But it seems that works under Debian with KVM only. By switching to XEN i got erroes
Failed to bind port 90b1c2da-417e-4ce7-be48-c4d1f4adc596 on host sackgesicht for vnic_type normal using segments [{'segmentation_id': None, 'physical_network': u'ovsbr1', 'id': u'56ecd982-198f-41f0-ab6a-be1df5d6daca', 'network_type': u'flat'}]
2017-03-19 23:19:24 UTC libxl: error: libxl_exec.c:118:libxl_report_child_exitstatus: /etc/xen/scripts/vif-bridge online [24558] exited with error status 1
2017-03-19 23:19:24 UTC libxl: error: libxl_create.c:1383:domcreate_attach_vtpms: unable to add nic devices
2017-03-19 23:20:36 UTC libxl: error: libxl_exec.c:118:libxl_report_child_exitstatus: /etc/xen/scripts/vif-bridge online [25638] exited with error status 1
2017-03-19 23:20:36 UTC libxl: error: libxl_create.c:1383:domcreate_attach_vtpms: unable to add nic devices
2017-03-19 23:57:18 UTC libxl: error: libxl_dm.c:1964:kill_device_model: Device Model already exited
2017-03-20 01:38:04 UTC libxl: error: libxl_event.c:683:libxl__ev_xswatch_deregister: remove watch for path @releaseDomain: Bad file descriptor
2017-03-20 05:20:42 UTC libxl: error: libxl_event.c:683:libxl__ev_xswatch_deregister: remove watch for path @releaseDomain: Bad file descriptor
2017-03-20 06:57:17 UTC libxl: error: libxl_event.c:683:libxl__ev_xswatch_deregister: remove watch for path @releaseDomain: Bad file descriptor
can't add tap802da6a9-90 to bridge br-int: Operation not supported
XEN is configured to use openvswitch by self. But something calls the wrong scripts. And if I hack the scipts by myself, then neutron puts the interfaces into the wrong bridge :/
You may install Mitaka with OVS by default via any RH's deployment approach :- packstack (yet completely functional) or TripleO on CentOS 7.X.
Configuration, though not installation, is found in the networking guide. For installation, perhaps the Ubuntu wiki helps.