Update service name for Sahara, retain compatibility
Update service name for Sahara, retain compatibility

Sahara changed the service name from data_processing to data-processing
in Kilo. Change the default expected value, but allow the usage of the
old name as long as the last old version using it is supported.

Change-Id: I80cd55e99de8f53aaf2bad109fcc939583095994

danielmellado/tempest,danielmellado/tempest,eggmaster/tempest,eggmaster/tempest