Use a compute service type from tempest.conf

Auto negative test generator is using static service type 'compute',
but EndpointNotFound happens when customizing compute service type
on Keystone.
This patch fixes the problem by using a compute service type from
tempest.conf.

Change-Id: I5fcf53cc9a24bf4f2a00f11540bd87932212933f
diff --git a/tempest/api/compute/admin/test_flavors_negative.py b/tempest/api/compute/admin/test_flavors_negative.py
index 5bc3d10..fb27360 100644
--- a/tempest/api/compute/admin/test_flavors_negative.py
+++ b/tempest/api/compute/admin/test_flavors_negative.py
@@ -18,9 +18,13 @@
 from tempest.api.compute import base
 from tempest.api_schema.request.compute.v2 import flavors
 from tempest.common.utils import data_utils
+from tempest import config
 from tempest import exceptions
 from tempest import test
 
+
+CONF = config.CONF
+
 load_tests = test.NegativeAutoTest.load_tests
 
 
@@ -106,5 +110,5 @@
 class FlavorCreateNegativeTestJSON(base.BaseV2ComputeAdminTest,
                                    test.NegativeAutoTest):
     _interface = 'json'
-    _service = 'compute'
+    _service = CONF.compute.catalog_type
     _schema = flavors.flavor_create
diff --git a/tempest/api/compute/flavors/test_flavors_negative.py b/tempest/api/compute/flavors/test_flavors_negative.py
index cae1ac4..83f8e19 100644
--- a/tempest/api/compute/flavors/test_flavors_negative.py
+++ b/tempest/api/compute/flavors/test_flavors_negative.py
@@ -15,23 +15,26 @@
 
 from tempest.api.compute import base
 from tempest.api_schema.request.compute.v2 import flavors
+from tempest import config
 from tempest import test
 
 
+CONF = config.CONF
+
 load_tests = test.NegativeAutoTest.load_tests
 
 
 @test.SimpleNegativeAutoTest
 class FlavorsListWithDetailsNegativeTestJSON(base.BaseV2ComputeTest,
                                              test.NegativeAutoTest):
-    _service = 'compute'
+    _service = CONF.compute.catalog_type
     _schema = flavors.flavor_list
 
 
 @test.SimpleNegativeAutoTest
 class FlavorDetailsNegativeTestJSON(base.BaseV2ComputeTest,
                                     test.NegativeAutoTest):
-    _service = 'compute'
+    _service = CONF.compute.catalog_type
     _schema = flavors.flavors_details
 
     @classmethod