Allow for global datasources preference from config

Allows to define a global preference for metric datasources with the
ability for strategy specific overrides. In addition, strategies which
do not require datasources have the config options removed this is
done to prevent confusion.

Some documentation that details the inner workings of selecting
datasources is updated.

Imports for some files in watcher/common have been changed to resolve
circular dependencies and now match the overall method to import
configuration.

Addtional datasources will be retrieved by the manager if the
datasource throws an error.

Implements: blueprint global-datasource-preference
Change-Id: I6fc455b288e338c20d2c4cfec5a0c95350bebc36

watcher/datasources/base.py

@@ -0,0 +1,100 @@
+# -*- encoding: utf-8 -*-
+# Copyright 2017 NEC Corporation
+#
+# 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 abc
+
+
+class DataSourceBase(object):
+
+    METRIC_MAP = dict(host_cpu_usage=None,
+                      host_memory_usage=None,
+                      host_outlet_temp=None,
+                      host_inlet_temp=None,
+                      host_airflow=None,
+                      host_power=None,
+                      instance_cpu_usage=None,
+                      instance_ram_usage=None,
+                      instance_ram_allocated=None,
+                      instance_l3_cache_usage=None,
+                      instance_root_disk_size=None,
+                      )
+
+    @abc.abstractmethod
+    def statistic_aggregation(self, resource_id=None, meter_name=None,
+                              period=300, granularity=300, dimensions=None,
+                              aggregation='avg', group_by='*'):
+        pass
+
+    @abc.abstractmethod
+    def list_metrics(self):
+        pass
+
+    @abc.abstractmethod
+    def check_availability(self):
+        pass
+
+    @abc.abstractmethod
+    def get_host_cpu_usage(self, resource_id, period, aggregate,
+                           granularity=None):
+        pass
+
+    @abc.abstractmethod
+    def get_host_memory_usage(self, resource_id, period, aggregate,
+                              granularity=None):
+        pass
+
+    @abc.abstractmethod
+    def get_host_outlet_temp(self, resource_id, period, aggregate,
+                             granularity=None):
+        pass
+
+    @abc.abstractmethod
+    def get_host_inlet_temp(self, resource_id, period, aggregate,
+                            granularity=None):
+        pass
+
+    @abc.abstractmethod
+    def get_host_airflow(self, resource_id, period, aggregate,
+                         granularity=None):
+        pass
+
+    @abc.abstractmethod
+    def get_host_power(self, resource_id, period, aggregate, granularity=None):
+        pass
+
+    @abc.abstractmethod
+    def get_instance_cpu_usage(self, resource_id, period, aggregate,
+                               granularity=None):
+        pass
+
+    @abc.abstractmethod
+    def get_instance_ram_usage(self, resource_id, period, aggregate,
+                               granularity=None):
+        pass
+
+    @abc.abstractmethod
+    def get_instance_ram_allocated(self, resource_id, period, aggregate,
+                                   granularity=None):
+        pass
+
+    @abc.abstractmethod
+    def get_instance_l3_cache_usage(self, resource_id, period, aggregate,
+                                    granularity=None):
+        pass
+
+    @abc.abstractmethod
+    def get_instance_root_disk_size(self, resource_id, period, aggregate,
+                                    granularity=None):
+        pass