[api_versions] Allow to use unknown services

Method `rally.osclients.services` returns only known services(services which
names and service types are hardcoded in rally.consts module).
Since api_versions allows to setup non-default service type for services, we
should take this into account in `required_services` validator.

Also, this patch:
 - moves ability to setup services via service_name only for admin users
 - removes versioned services from consts, since they are not"real"
   (Nova V3 was removed before it released, Nova V21 is now hosted under
   Nova service...)

Change-Id: I0c86c0c42ee7e25b92bd322c2e116ce25308a93a

rally/consts.py

@@ -91,10 +91,7 @@ class _Service(utils.ImmutableMixin, utils.EnumMixin):
 
     NOVA = "nova"
     NOVA_NET = "nova-network"
-    NOVAV21 = "novav21"
-    NOVAV3 = "novav3"
     CINDER = "cinder"
-    CINDERV2 = "cinderv2"
     MANILA = "manila"
     EC2 = "ec2"
     GLANCE = "glance"
@@ -118,7 +115,6 @@ class _ServiceType(utils.ImmutableMixin, utils.EnumMixin):
     """OpenStack services types, mapped to service names."""
 
     VOLUME = "volume"
-    VOLUMEV2 = "volumev2"
     SHARE = "share"
     EC2 = "ec2"
     IMAGE = "image"
@@ -126,8 +122,6 @@ class _ServiceType(utils.ImmutableMixin, utils.EnumMixin):
     ORCHESTRATION = "orchestration"
     IDENTITY = "identity"
     COMPUTE = "compute"
-    COMPUTEV21 = "computev21"
-    COMPUTEV3 = "computev3"
     NETWORK = "network"
     DNS = "dns"
     METERING = "metering"
@@ -144,10 +138,7 @@ class _ServiceType(utils.ImmutableMixin, utils.EnumMixin):
     def __init__(self):
         self.__names = {
             self.COMPUTE: _Service.NOVA,
-            self.COMPUTEV21: _Service.NOVAV21,
-            self.COMPUTEV3: _Service.NOVAV3,
             self.VOLUME: _Service.CINDER,
-            self.VOLUMEV2: _Service.CINDERV2,
             self.SHARE: _Service.MANILA,
             self.EC2: _Service.EC2,
             self.IMAGE: _Service.GLANCE,