Rename Meta-Action to Action

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 Meta-Action to Action

Partially implements: blueprint glossary-related-refactoring

Change-Id: Ie67b800332179be93718030ddd7a36ddc76a544c

watcher/decision_engine/solution/base.py

@@ -57,6 +57,6 @@ class Solution(object):
             "Should have implemented this")  # pragma:no cover
 
     @abc.abstractproperty
-    def meta_actions(self):
+    def actions(self):
         raise NotImplementedError(
             "Should have implemented this")  # pragma:no cover