Refactor to improve modularity, scalability, OOP

* each service class was moved to a new file
* Service and VersionedService were moved from api_discovery to service_base.py
* api_discovery.py is removed and methods for discovery were moved to a newly
  created class Services - class holds methods related to instantiating
  services, discovering their versions and extensions, configuring them
* constants were moved to an independent file - constants.py

Change-Id: I00880f4bd30cc4d1609c20aecca820854312b1e7

config_tempest/constants.py

@@ -0,0 +1,67 @@
+# Copyright 2013, 2016, 2018 Red Hat, Inc.
+# All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import logging
+import os
+
+LOG = logging.getLogger(__name__)
+
+# Get the current tempest workspace path
+TEMPEST_WORKSPACE = os.getcwd()
+
+DEFAULTS_FILE = os.path.join(TEMPEST_WORKSPACE, "etc",
+                             "default-overrides.conf")
+DEFAULT_IMAGE = ("http://download.cirros-cloud.net/0.3.5/"
+                 "cirros-0.3.5-x86_64-disk.img")
+DEFAULT_IMAGE_FORMAT = 'qcow2'
+
+# services and their codenames
+SERVICE_NAMES = {
+    'baremetal': 'ironic',
+    'compute': 'nova',
+    'database': 'trove',
+    'data-processing': 'sahara',
+    'image': 'glance',
+    'network': 'neutron',
+    'object-store': 'swift',
+    'orchestration': 'heat',
+    'share': 'manila',
+    'telemetry': 'ceilometer',
+    'volume': 'cinder',
+    'messaging': 'zaqar',
+    'metric': 'gnocchi',
+    'event': 'panko',
+}
+
+# what API versions could the service have and should be enabled/disabled
+# depending on whether they get discovered as supported. Services with only one
+# version don't need to be here, neither do service versions that are not
+# configurable in tempest.conf
+SERVICE_VERSIONS = {
+    'image': {'supported_versions': ['v1', 'v2'], 'catalog': 'image'},
+    'identity': {'supported_versions': ['v2', 'v3'], 'catalog': 'identity'},
+    'volume': {'supported_versions': ['v2', 'v3'], 'catalog': 'volumev3'}
+}
+
+# Keep track of where the extensions are saved for that service.
+# This is necessary because the configuration file is inconsistent - it uses
+# different option names for service extension depending on the service.
+SERVICE_EXTENSION_KEY = {
+    'compute': 'api_extensions',
+    'object-store': 'discoverable_apis',
+    'network': 'api_extensions',
+    'volume': 'api_extensions',
+    'identity': 'api_extensions'
+}