Rename Mapper to Mapping

Some Python class and packages need to be renamed
for a better compliance with the shared terminology
which provides a better understanding of Watcher
objects and components by every contributor.

This patchset is there to change mapper to mapping

Partially implements: blueprint glossary-related-refactoring

Change-Id: Ieaca42431322ce40d87de147ac0b46a1f446f390

watcher/applier/execution/executor.py

@@ -17,10 +17,8 @@
 # limitations under the License.
 #
 from oslo_log import log
-
-from watcher.applier.mapper.default import DefaultActionMapper
-
 from watcher.applier.execution.deploy_phase import DeployPhase
+from watcher.applier.mapping.default import DefaultActionMapper
 from watcher.applier.messaging.events import Events
 from watcher.common.messaging.events.event import Event
 from watcher.objects import Action

watcher/applier/mapping/default.py

@@ -16,15 +16,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-
-
-from watcher.applier.mapper.base import BaseActionMapper
+from watcher.applier.mapping.base import BaseActionMapper
 from watcher.applier.primitives.change_nova_service_state import \
     ChangeNovaServiceState
 from watcher.applier.primitives.migration import Migrate
 from watcher.applier.primitives.nop import Nop
 from watcher.applier.primitives.power_state import ChangePowerState
-
 from watcher.common.exception import ActionNotFound
 from watcher.decision_engine.planner.default import Primitives