Removed event_id property from config

Event_id was used in some of the stacktach smoke tests,
but it was very cumbersome to keep updating the event_id every
month as the data gets purged after 30 days. Hence, removing it
from here & updated tests with a new method

Change-Id: Id33a29576391779818efd510608f95c93eeb79f8

cloudcafe/stacktach/config.py

@@ -33,10 +33,6 @@ class StacktachConfig(ConfigSectionInterface):
 
     SECTION_NAME = 'stacktach'
 
-    @property
-    def event_id(self):
-        return self.get('event_id')
-
     @property
     def url(self):
         return self.get('url')

configs/stacktach/default.config

@@ -3,7 +3,6 @@ serialize_format=json
 deserialize_format=json
 
 [stacktach]
-event_id=<id of an event>
 url=<stacky url>
 db_url=<stacktach db api url>
 days_passed=<number of days passed>