Merge device specific keywords to retrieve entity ownership data

Merge device specific keywords to retrieve entity ownership data

Keywords 'Get_Owner_And_Candidates_For_Device_Singleton_{device_type}'
defined for netconf, bgpcep, sxp are the same except for prefix/suffix
added to the device name. Create a dictionary for the prefix/suffix
and share the same keyword Get_Owner_And_Candidates_For_Device_Singleton.

The keyword didn't support OpenFlow device type before, because there
was no keyword specific to the OpenFlow device type, but it is
supported now.

This change also removes the odl-general-entity prefix/suffix for
bgpcep & sxp because the entity name does not include the prefix
with the new entity owner RPC - netconf does not have it.

Signed-off-by: Sangwook Ha <sangwook.ha@verizon.com>
Change-Id: I5181e2f9f531835310714789ece8df9634ee118f