add script to generate test event data

similar to make_test_data.py, this script generates a set of events
and writes them to the database (defined in ceilometer.conf).

configurable options:
- start - number of days in past to start test data
- end - number of days into the future to start test data
- interval - period between events, in minutes
- event_types - number of unique event_types

Change-Id: I80e023a82f7d5129649a5b1de5256e41e901e3c1
Merge "add script to generate test event data"