At the moment, all data is retained infinitely. This change allows users
to specify a default_retention_hours (defaults to 0 meaning unlimited
retention) in the influxdb section of monasca persister configuration so
that new projects are automatically assigned this retention policy when
the given hour is greater than 0 to preserve original behaviour.
Story: 2006331
Task: 37234
Change-Id: I4136df1d43954eb026a104f3f85b3a58197f5435
97aab2f004